I think I might be switching from Opera to FireFox for my default web browser. Why you ask? Well there still are some things about it that I find slightly annoying, but I found an extension that makes it almost as fast as Opera. I also like a few other extensions that exist. Most are to make it perform like Opera, but others are definitely just useful. I'd still have to say that out of the box, Opera wins hands down.

My installed extensions which Opera has by default:

• All-In-One Sidebar
• Answers - click on a word to look it up in a dictionary
• Fasterfox - Makes FireFox faster at rendering pages (which helps a lot with the cache, cuz FireFox doesn't use it much)
• Firefox showcase - Shows thumbnail previews of the pages you have opened. This one is a little better than the Opera one in the sense that you can see them all at once, however you have to push F12 to get it to show and it's in a separate window, both of which I don't like.
• Mouse Gestures
• Tab Mix Plus - An extension to make the tabs behave like Opera

Other extensions I have that I find useful

• ColorZilla (a little eye dropper utility)
• Console2 (I'm still not sure what this does)
• DownThemAll (A tool to download all of a certain type of file from a page. I have yet to use it though)
• ErrorZilla Mod (Not sure what this one is either...)
• FireFTP (A basic integrated FTP client)
• TimeStamp Converter
• Web Developer (Best. extension. ever.)
• HTML Validator (Second best extension)
• MeasureIt (Just a little ruler utility to measure pixels)

What I like better about Opera:

• Better popup blocker (popups keep popping up all over the place in FireFox even though I have them disabled)
• Faster browsing. Yep, nothing beats Opera still. But FireFox is close with my "Fasterfox" extension.
• Opera's "progress bar" is far superior to anything I have seen in any other browser ever.
• Pushing the back button to a page with POST data does not require a re-submission of this data, meaning that the page is loaded purely from the cache. You therefore don't lose the information you put into forms when pushing the "back" button.
• Better CSS support (however FireFox is very close)
• Full RSS/feed support (FireFox just has "live bookmarks" which don't compare to Opera)
• Opera's download manager is WAY better than FireFox's (which pops up in a new window on top of it all, blegh!)
• Everything is always in one window. No use cluttering up your taskbar. The Tab Mix Plus extension comes close, but things still pop up in separate windows from time to time.
• Integrated torrent downloading client (which I rarely used)
• Integrated e-mail client (which I never used, but it's still a very good feature)

What I like better about FireFox:

• It's open source
• Better script rendering (i.e. JavaScript works better)
• Extensions! (The Opera Widgets, however more secure, are useless pieces of crap)
• Slightly more customizable

So besides the popup blocker, the progress bar, and requiring a re-sending of the POST data, I don't think I would miss Opera too much. I'm going to use FireFox for a while and see how I like it.