I was hesitant to upgrade Firefox because I knew it would break some extensions, but the supposed speed and security improvements were tempting so I went for it anyway. It installed quickly, and on first run checked all the extensions, automatically disabling / downloading new versions as necessary. This Just Worked, happily.
Is good. It seems faster than 1.5. I tend to have 15-20 tabs open at any particular time, which sometimes slowed down FF1.5 considerably. FF2 seems to handle them without a problem, which is great. Page loads seem subjectively faster, but I’m aware there are plenty of other factors which could be fooling me there. FF2 looks much nicer than 1.5, too. I always thought the default theme was ugly and never found anything much better in custom themes (with the possible exception of the Opera theme, but that caused problems with Options dialogs). The new silver / grey theme looks much classier, imho.
Most of the broken extensions had alternatives:
Tab Mix Plus – adds many useful options to FF’s tabbed browsing feature, such as a maximum and minimum tab size, multiple lines of tabs instead of a scrolling bar and close-tab buttons in reasonable locations. The official version isn’t yet compatible, but the Release Candidate seems to work ok, despite a couple of bugs with re-ordering tabs.
Resizable textarea – allows any text field to be resized, and comes in useful surprisingly often (particularly on blogger.com comment boxes). A compatible version can be found in the comments here.
Compact Menu – removes the pointless ‘File, Edit’ etc. menu bar and replaces it with a drop-down list which can be placed next to the address bar. Not updated for FF2, but there’s a compatible version available here.
Paste and Go – just a little thing, but one-click pasting and loading of URLs is surprisingly pleasing. The old version has been replaced with Paste and Go 2.
I can’t think of the last time a site was broken in Firefox. I think this is probably to do with the great rendering engine, although it’s possible that most of the sites I visit these days are the kind that design for FF anyway. I have the occasional problem with Windows Media Player files refusing to load, but that’s all. It’s easily a full IE replacement. I don’t have any actual problems with IE7, but extensions make FF2 the more productive of the two.