Firefox 143 Review: AI Sidebar with Copilot, Pinned Apps, and Privacy Wins

Mozilla’s latest stable build, Firefox 143, lands as a pragmatic — and at times polarizing — update: it brings a sidebar shortcut to Microsoft Copilot and the wider AI-chat ecosystem while doubling down on user-facing privacy controls, accessibility fixes, and platform-specific media and web-app features. The release stitches together convenience features that many users expect from modern browsers (pinned web apps and richer media codecs) with incremental but meaningful hardening against tracking techniques, new private-mode behaviors, and developer-facing CSS and console improvements. The net effect is a release that keeps Firefox competitive on features while trying to preserve the privacy-first posture that sets it apart from some rivals.

Background / Overview​

Firefox 143 continues Mozilla’s steady cadence of biweekly-ish releases and follows the project’s recent focus on integrating optional AI services into the browser UI. This update is notable because it places AI chat access (including the ability to reach Microsoft Copilot) directly in the browser sidebar, while also shipping several privacy-focused settings and quality-of-life features that change behavior for both everyday users and power users.
The release is a hybrid: some items are developer-facing rendering and API changes, while others are user-facing features and toggles. Several features are being rolled out progressively and some are gated behind experimental flags or limited by install channel (for example, certain features are not available when Firefox is installed from the Microsoft Store). The build also contains platform-specific updates such as a new audio codec on supported platforms and accessibility improvements for Windows.

---

What’s new in Firefox 143 — quick summary​

• AI sidebar with Copilot access: Users can open an AI chat panel in the sidebar and select among available chatbot providers; Microsoft Copilot can be used through this sidebar experience.
• Pin websites as apps on Windows: Firefox adds the ability to pin sites and run them as simplified standalone windows (a progressive web app-like experience), with the caveat that the Microsoft Store build is excluded for now.
• Expanded Fingerprinting Protection: Firefox reports constant values for more system attributes, aiming to reduce the entropy sites can use to uniquely identify users.
• Private Browsing: auto-delete downloaded files: A new option lets users choose to have files downloaded during a private session removed automatically when the session ends.
• Camera preview in permission prompts: When a site requests camera access, the permission prompt now shows a live preview to help select among multiple cameras.
• xHE-AAC playback support: Firefox now supports xHE-AAC on Windows 11 (22H2+), macOS, and Android 9+, enabling better low-bitrate audio behavior and potentially improved streaming compatibility.
• Windows UI Automation improvements: Better support for assistive tools such as Narrator and Voice Access through updated Windows UI Automation hooks.
• Smarter address bar: The address bar (omnibox) now surfaces richer results in some regions — for example, showing event dates where applicable.
• Developer updates: Ungrouped console messages, improved CSS Grid sizing to align with standards, a ::details-content pseudo-element, and expanded <input type="color"> support for modern color formats.

---

Deep dive: Copilot in the sidebar — what’s actually happening​

What users will see​

Firefox 143 exposes an AI chat sidebar. Within that sidebar, users can select from a set of chatbot providers. Microsoft Copilot is among the providers that users can run from the sidebar, and clicking the Copilot entry launches the Copilot web experience inside the panel. The UI is designed to make switching between chat providers quick and convenient.

Technical nature of the integration​

This is not a native, deeply embedded Copilot engine inside Firefox. Rather, the browser provides a sidebar container and UI shortcuts that surface the Copilot web app (or other third‑party chat web apps) in a quick-access panel. The web-based Copilot runs as a remote service; any advanced browser-to-AI integration (for example, the browser exposing the contents of the active tab automatically to Copilot or granting OS-level integration) is not part of the core Firefox-side capability in this release.

Limitations and caveats​

• The sidebar acts like a convenient container or shortcut to the Copilot web app; features that require tight browser-to-service integration (such as automatic page summarization without pasting or explicit share actions) may be limited compared with a first-party integration.
• Some functionality requires signing into a Microsoft account, and feature availability can depend on subscription level or account entitlements.
• The degree of personalization, chat history syncing, and extended capabilities depend on Copilot’s server-side rules and account state — Firefox itself does not add server-side AI capabilities.
• Hidden or experimental preferences control which chat providers appear; advanced users can toggle availability through internal config flags.

Privacy implications​

Using Microsoft Copilot via the sidebar means you are interacting with a Microsoft-hosted service. Any prompts, uploads (images, documents), and the conversation itself are transmitted to Microsoft servers. That brings the standard privacy trade-offs of using third-party AI services:

• Data leaving the browser to Copilot is governed by Microsoft’s terms and data-handling policies, not Mozilla’s.
• If you’re privacy-conscious, you should treat Copilot interactions as cross-service communications and consider whether to log in or to avoid sharing sensitive data in prompts.
• For organizations, there are additional identity and compliance considerations when employees use Copilot with company data.

Bottom line: the sidebar makes Copilot more convenient, but it does not change the underlying data flows or guarantee that interactions remain private to the local machine.

---

Web apps / pinned sites on Windows — parity with other browsers​

Firefox 143 adds the option to pin websites as standalone apps on Windows and open them in simplified windows without the full browser chrome — a familiar feature for users coming from Chrome or Edge. These site-as-app windows preserve add-ons and can be taskbar-pinned for quick access.
Important platform note: installs of Firefox from the Microsoft Store do not yet get this pin-as-app capability. This distinction matters because the Store package uses different packaging and distribution policies that can limit certain system integration points.
Practical takeaways:

• Use the “Install site as app” option when you want a lightweight, dedicated window for a web app.
• Test add-on behavior in pinned windows if you rely on browser extensions for functionality.
• Enterprises that deploy Firefox via Store packaging should test for parity before recommending pinned sites to users.

---

Stronger fingerprinting protection — the technical approach​

Firefox 143 expands its Fingerprinting Protection by reporting constant or standardized values for additional system attributes. The strategy is to reduce the amount of unique information websites can obtain about a device.
How it works in practice:

• Instead of exposing raw, high-entropy details (for example, precise GPU identifiers, hardware metrics, or subtle browser behavior differences), Firefox maps several attributes to common or constant values.
• The approach increases the “blend” between users, making it harder for trackers to single out a device based on combined attributes.

Limitations to be aware of:

• No browser can completely eliminate fingerprinting; the goal is to lower entropy and increase cost/complexity for trackers.
• Some legitimate web apps rely on precise system information for diagnostics or compatibility; hardened fingerprinting settings can occasionally break such sites.
• Progressive deployment and feature flags mean that behavior may vary by user, channel, or region.

For privacy-minded users, this expansion is a meaningful improvement. For developers and site operators, expect to test compatibility if you serve device-specific functionality.

---

Private browsing and downloaded files — auto-delete behavior​

Firefox 143 introduces a private browsing option to automatically delete files downloaded during a private session when that session closes. This is a useful change for users who want their private windows to leave no persistent artifacts on disk after closing.
Key details:

• The browser prompts users on the first download in private mode with options to keep or remove downloads when the private session ends.
• There is also a permanent setting in Firefox’s privacy preferences to always auto-delete private-mode downloads, offering convenience for users who prefer the behavior by default.
• This behavior addresses a long-standing privacy gap: previously, private browsing cleared history and cookies but downloaded files remained on disk unless manually deleted.

User guidance:

• When downloading inside Private Window, respond to the keep/delete prompt as desired.
• To set the default behavior, open Privacy settings and change the “Delete private browsing downloads on exit” preference.

---

Camera preview in permission prompts — small but practical​

The permission dialog for camera access now shows a live preview of the selected camera. This is a helpful UX quality-of-life improvement that makes it easy to choose the correct device when multiple webcams are attached, and it reduces the need to allow access and then switch devices from within the site.
Accessibility and security benefits:

• Users with multiple cameras (internal, external, virtual) can confirm the chosen device visually before granting access.
• This reduces mistaken permissions grants and minimizes friction for video conferencing and content capture scenarios.

---

xHE-AAC support — why it matters​

Firefox 143 adds playback support for xHE‑AAC on Windows 11 (22H2 and later), macOS, and Android 9+. xHE‑AAC is an audio codec optimized for a wide range of bitrates and provides improved audio quality at low bandwidth, which can be especially useful for streaming services that want to conserve bandwidth without sacrificing voice clarity.
Platform considerations:

• On Windows 11, the OS-level support requirement (22H2+) means older Windows builds won’t benefit.
• Support on macOS and Android broadens compatibility for cross-platform web audio playback.

Practical benefits:

• Better low-bitrate audio quality for streaming services.
• Potentially fewer codec fallbacks and smoother playback experiences across platforms.

---

Accessibility: Windows UI Automation improvements​

Firefox 143 enhances Windows UI Automation bindings, improving interoperability with assistive technologies like Narrator and Voice Access. These updates aim to make Firefox more navigable and usable for people who rely on screen readers or voice control.
What users and admins should expect:

• More reliable role, state, and name exposure to assistive tech.
• Improved keyboard and focus behavior in some UI areas.
• Enterprises should validate custom accessibility workflows after updating.

---

Smarter address bar results and developer tooling improvements​

Firefox’s address bar now surfaces richer, contextual results in certain regions — for example, showing event dates or related quick actions. On the developer side, console message grouping options have been refined (ungrouped messages are easier to inspect), CSS Grid sizing aligns more closely with the spec, and <input type="color"> now accepts a broader set of color format inputs (including color functions and named colors, with values normalized back to hex).
Developer-focused changes include:

• ::details-content pseudo-element added and enabled, giving finer control over styling collapsed content.
• Grid sizing algorithm update that fixes rendering of percentage-row grids and items with aspect ratios.
• New storage API helper for add-on developers to list keys in storage areas.

These changes improve standards compliance and debugging ergonomics.

---

Critical analysis: strengths​

• Practical privacy advances: The expanded fingerprinting protection and private-mode download auto-delete demonstrate that Mozilla remains committed to privacy improvements that have real user impact.
• Accessibility and platform parity: UI Automation updates and xHE‑AAC support show attention to platform parity and inclusiveness.
• User choice with AI: By exposing multiple chat providers in the sidebar and making AI features opt-in, Firefox preserves user control rather than forcing a single provider; the sidebar model supports choice and competition.
• Developer-focused updates: CSS Grid alignment and console improvements address real pain points developers have faced when testing and debugging cross-browser layouts.
• PWA-like pinned site support: Pinned-site windows close functional gaps between Firefox and Chromium-based browsers, improving workflow continuity for users who run web apps as pseudo-native apps.

---

Critical analysis: risks and weaknesses​

• Superficial AI integration risk: Packaging Copilot (and other chat services) in a sidebar that simply hosts the web app may be perceived as cosmetic. Users expecting deep integration (e.g., automatic page reading, direct DOM access) will find the experience less integrated than competing first-party implementations.
• Privacy trade-offs with third-party AI: Convenience comes with data-sharing trade-offs. Using Copilot routes data to Microsoft’s infrastructure and subjects that data to Microsoft policies. For some users, the convenience is unacceptable — and the risk increases if corporate or sensitive content is pasted or uploaded to the chat.
• Fragmentation across install channels: Feature differences between the classic installer and the Microsoft Store build complicate messaging and enterprise deployment pipelines; organizations using the Store version may miss features and need to account for that in user support.
• Potential fingerprinting arms race: While the expanded fingerprinting protection reduces entropy, trackers will continue to evolve. Browser-side mitigations must be accompanied by ecosystem and policy work to avoid feature breakage for legitimate apps.
• Unclear long-term roadmap for AI: Mozilla’s careful approach to AI (opt-in, provider choice) is principled, but the lack of a single, tightly integrated on-device model or clear roadmap for local AI capabilities may leave power users wanting more seamless offline-first AI that preserves privacy.

---

Practical recommendations​

For everyday users​

• If you value convenience: try the AI sidebar but be cautious about pasting or uploading sensitive content to Copilot without understanding the account and data policies.
• If you prioritize privacy: disable AI features via the experimental preferences or use the classic installer and adjust the AI-related about:config keys to false. Use private browsing auto-delete if you frequently download ephemeral files.

For power users and developers​

• Test your sites in Firefox 143 for grid layout differences and color input handling. Expect some layout behavior changes due to the updated grid sizing algorithm.
• Use the new developer console behaviors to inspect formerly grouped messages more easily.
• If you distribute packaged web apps for Windows users, test pinned-site behavior and how add-ons behave in that simplified window mode.

For IT administrators and enterprise teams​

• Evaluate the Microsoft Store install vs classic MSI/EXE deployment: the Store build may lack the new pinned-site capability.
• Review privacy and compliance policies before permitting Copilot use for employees; consider conditional access policies and training to prevent sharing of PII or proprietary content with third-party AI services.
• Test accessibility workflows with the new Windows UI Automation improvements to confirm third-party assistive technologies behave as expected.

---

How to enable, disable, or manage the AI sidebar (practical steps)​

• Update Firefox to version 143 or ensure you are on the relevant Release/Beta channel that includes the feature.
• Open Settings and check the Nightly/Experimental features area if the AI chat does not appear by default (some features are progressively rolled out).
• To remove or disable AI providers:
• Advanced users can use about:config to search for AI-related preferences (search for keys beginning with browser.ml.chat or similar) and toggle them off.
• For enterprise policy control, test the available administrative policies to see whether the AI features can be centrally-controlled before broad deployment.

---

Final assessment — where Firefox 143 fits in the browser landscape​

Firefox 143 is an incremental but carefully balanced release. It blends practical user-facing features (pinned apps, better audio codec support, camera preview) with meaningful privacy hardening and accessibility improvements. The introduction of a sidebar-accessible Microsoft Copilot — alongside other chatbot options — is a clear nod to user demand for embedded AI tools in browsers, but Mozilla’s implementation intentionally prioritizes user choice and optionality over forced, deep integrations.
That choice is both Firefox’s strength and its constraint. By avoiding deep coupling with a single AI provider, Mozilla preserves privacy-oriented positioning and supports plurality; but the trade-off is a less seamless AI experience compared with browsers that offer vertically integrated Copilot-like experiences. For privacy-first users and developers who value standards compliance and control, Firefox 143 continues to be a solid, responsible browser update. For users seeking the most tightly integrated AI workflow, the experience may feel more like a convenient shortcut than a fully native assistant.
Overall, Firefox 143 demonstrates Mozilla’s pragmatic strategy: adopt modern conveniences where they add value, but preserve control, privacy, and standards compatibility rather than hand over the browser to a single cloud provider. The release reduces some privacy gaps (notably downloads in private browsing) and fixes platform pain points, even as it opens the door to new conversations about AI, data flow, and platform integration.

---

Source: Windows Report Mozilla launches Firefox 143 with Copilot and new privacy tools