Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
The longer you use Firefox, the more little things you'll collect that make your online life easier: bookmarks (known as "Favorites" to recovering Internet Explorer users), a History file listing sites you've visited, saved login names and passwords, and so on. Firefox puts almost all of this information, along with your extensions, browser plug-ins, cache and configuration files, in one place: your profile folder.
Even if you're not much of a techie, it's a good idea to know where to find your profile, what types of files you'll find there, and how you can protect them against mishaps.
Meet Your Profile
Depending on your operating system, you'll find a copy of your Firefox profile folder in different places:
Mac OS X: ~/Library/Application Support/Firefox/Profiles/
Windows XP/2000: C:\Documents and Settings\[your user name]\Application Data\Mozilla\Firefox\Profiles\
(Note: You may not see the Application Data folder where it's supposed to be. That's because Windows hides this folder, and many others, by default. To see it, click Tools on your Windows Explorer menu, click Folder Options, select the View tab, click the "Show hidden files and folders" radio button, and click OK.)