Yep, whether Firefox is the best or not is open to debate (I think it is!) but one thing is pretty much certain - It's better than Opera.
Firefox has a built in downloader and though the mail isn't built in it works well with the Thunderbird Mail Client. You can customise it much more than you can Opera and it doesn't have the annoying ad-bar that you get with the free version of Opera. It has a built in search for Google, Yahoo, eBay, Amazon and you can install a search for
Abandonia!. You can also easily set up key words for your favourite sites and I find the bookmarks toolbar much more accessible in Firefox than in Opera. It will also autocomplete addresses, which sometimes ends in some very strange results but most of the time it works fine. For example - just type abandonia and it will add the www. and .com to the address. And in my experience, it's much faster than Opera. It's also pleasant to look at while Opera has windows and ads taking up most of your browsing space.
Think that proves the point!
Oh, and this should really be in Technical, not Blah, Blah, Blah!