At least in my opinion, it's unnecessary bloat - just like that video chat thing they added a couple months ago.
Remember when Firefox, the lean, scrappy browser, first came out and ran circles around the bloated Netscape browser/HTML editor/IM client/mail client/newsreader? The Firefox team seems to have forgotten.
If anyone is maintaining a "Firefox: Browser Only Edition" fork, I'd love to know about it so I could use that instead.