Firefox 157.0.1 Fixes Windows Backup Setup, macOS Downloads and a Moderate Security Flaw

Version 157 was a big redesign​

Firefox 157 is the release where Mozilla changed the browser's look. The Register reported that it introduced a new theme called "Nova," which in the release notes Mozilla calls "Firefox's biggest visual refresh in years." The same outlet noted that the new theme is the flagship here, and aside from that, the new features in this version are fairly modest.

Mozilla's developer documentation dates the release: Firefox 157 was released on September 29, 2026. Mozilla's security advisory for the follow-up is dated October 6, 2026, so 157.0.1 arrived about a week after the redesign. The Firefox 157.0.1 folder in Mozilla's public release archive contains Windows (32-bit, 64-bit and ARM64), macOS and Linux builds, with files stamped October 5. That tells you when the packages were built, not when a given PC will be offered the update.

Section summary: Firefox 157 brought the Nova redesign on September 29. Version 157.0.1 is the cleanup release for Windows, macOS and Linux about a week later.

The three bug fixes​

1. macOS: downloads failing in "ask where to save" mode​

This is the most specific of the three. PiunikaWeb quotes Mozilla's release notes: the fix covers downloads that failed on macOS when Firefox is set to "ask where to save files but doesn't have permission to access the Downloads folder."

The bug only showed up when two things were true at once:

• Firefox was set to ask where to save each file, rather than saving straight to a default folder.
• macOS had not given Firefox permission to access the user's Downloads folder.

PiunikaWeb says that in this case downloads would silently fail. Nothing suggests that every Mac download was broken, or that people who save straight to a default folder were affected. If you're on a Mac, use the "always ask" setting and noticed downloads disappearing this past week, this is probably the bug.

2. Sidebar stuck on Bookmarks or the AI chatbot​

The second fix is for the sidebar. According to PiunikaWeb, multiple users reported that the new collapsible sidebar kept locking up completely, getting stubborn whenever they tried switching between their Bookmarks and the AI Chatbot panel.

The release information frames this as affecting some users, apparently those with particular sidebar settings, rather than everyone. If you could open the sidebar but couldn't switch away from Bookmarks or the chatbot, version 157.0.1 is meant to fix that.

3. Windows: "Restore from Backup" missing during onboarding​

The third fix only affects Windows. PiunikaWeb reports that another Windows bug caused users to notice that the "Restore from Backup" option went missing entirely during the initial onboarding screen.

The problem was the missing button in first-run setup. Nothing in the evidence suggests backup files were lost or damaged, or that restoring a backup was broken generally. It still matters if you're setting up a new Windows 11 PC, or reinstalling Firefox after a clean Windows 10 install, and expect to restore your profile at the first screen. If you skipped that step because the option wasn't there, your backup file should still be wherever you saved it.

Section summary: Each bug is limited to one platform or one setup. The download bug is Mac-only and needs both conditions. The sidebar bug hit some users with certain settings. The onboarding bug is Windows-only and affected the button, not your data.

The security fix: CVE-2026-106016​

Mozilla Foundation Security Advisory 2026-104, published October 6, lists one fixed vulnerability:

Mozilla uses "moderate" for flaws that would otherwise be rated high or critical, but only work in uncommon, non-default configurations or need the user to take complicated or unlikely steps. The advisory gives no exploit details and says nothing about attacks in the wild, so don't read more into it than that. A moderate fix isn't an emergency, but it is a good reason not to put off a restart.

The two download-related problems in this release are separate issues: the Mac download bug and the file-handling security fix. They come from different bug reports and shouldn't be treated as the same thing.

How to update​

On Windows, Firefox normally updates itself in the background. To check manually:

1. Open Firefox.
2. Open the menu and go to Help → About Firefox (on a Mac, Firefox → About Firefox in the menu bar).
3. Let Firefox check for and download the update.
4. Restart when prompted and confirm the About window shows 157.0.1.

If the update doesn't install, the usual suspects are a locked install folder or a policy that disables updates. On managed machines, the update is pushed by IT rather than by you.

Mac users with the download problem: once you're on 157.0.1, it's still worth checking whether macOS has given Firefox access to your Downloads folder in its privacy settings. The update fixes Firefox's handling of the missing permission. It doesn't grant the permission for you.

Notes for IT admins​

Mozilla's enterprise release notes for Firefox 157 point out something that's easy to miss under the redesign news: Firefox ESR 140 goes out of support with this release. Firefox ESR 140.17.0 is its final build. Mozilla's enterprise notes also say that Firefox ESR 153 is the current ESR.

If you're still running ESR 140, there is no 157.0.1-style patch coming for you. Plan your move to ESR 153 now. If you run the regular release channel, 157.0.1 is a low-risk update: three narrow bug fixes and one moderate security fix.

Analysis: normal cleanup after a big redesign​

A point release a week after a major redesign is normal and expected (this part is general industry observation, not sourced). Big interface changes tend to break small things that test suites miss, and these bugs fit that pattern. The download bug involved macOS file permissions. The onboarding bug was a missing button in a first-run flow most people only see once. The sidebar bug depended on users' panel settings.

It's also worth being clear about what this release doesn't do. As PiunikaWeb notes, this minor release does not alter the underlying design changes. If you dislike Nova's styling, 157.0.1 won't change it.

Bottom line: Firefox 157.0.1 fixes three platform-specific bugs and one moderate security flaw. Install it, restart, and if you're an admin, make sure no machines are still on ESR 140.