Firefox doesn't have a built in newsreader but if you want one from Mozilla, it's called Thunderbird. It's ok.
I too prefer Outlook Express over any other mail reader, regardless of it's fallbacks. If you know the work arounds, OE is just as capable as any other reader. But unfortunately, OE will not work under Windows 7. But Windows Mail will. If you have access to a Vista computer, you can copy the complete content (all files and folders) inside %SystemDrive%\Program Files\Windows Mail\ folder in Windows Vista, and overwrite or replace the same folder on Windows 7.
Windows Mail is OE rebranded for Vista. This is not Windows Live Mail.
Good luck.