Always on the lookout for backup software (too many times i wish i had created them has taught me a hard lesson). Anyway.....I've came across MozBackup, a freeware backup tool for FireFox, Thunderbird, Mozilla, and even Netscape. Along with your bookmarks it also create copies of:

• History
• Cookies
• Saved Password
• even Downloaded file list + more

It is a Win32 app only though.