I switched from Opera (which I'd been using for ~six years) to Firefox. When I first started using Opera, it was before Firefox had tabbed browsing, which was the big deal breaker for me, but Opera also had a lot of really useful built-in features that Firefox didn't. Now, you can just download an add-on to give Firefox pretty much any feature you want. So I found a bunch that will make my Firefox more like my Opera. I switched to FF mostly because I was tired of so many sites not working quite right, if at all.
At the same time, I created a del.icio.us account to use instead of bookmarks in my browser. I still have to organize everything that I imported from my bookmarks, and get them all tagged right, and when I do, I'll link it here.
Lastly, I had been using LJ as my feedreeder until now. There's getting to be too many for that, so I'm using Firefox's Live Bookmark thingy - with an addon for easy viewing, so I've removed all my LJ feeds.