Wow.

[Quark]

I'm not clear on what extension are, though. They're like plugins? To add extra functionality?

Yeah. What is generally referred to as a "plugin" (I.E. Flash, Acrobat Reader) generally allows for a new type of webbrowsing (.pdfs, .swf, etc ...).

The "extensions" either change or add code for UI, Tab management, etc, directly on top of the Mozilla/Firebird code. For instance, Tabbrowser Extensions gives you a huge list of options, including stuff like loading new tabs in background (nice if you want to open up a bunch of news stories off a main site). There's even a Mouse Gestures one for people who use Opera and like that (I never liked them as I was always fighting my browsing style to not activate them erronously).

I've also uploaded my user.js, userChrome.css and userContent.css Here if you want to compare.