If you use Firefox and want to get a taste of what might be coming in future versions, one addon worth installing is Shawn Wilsher's Asynchronous Location Bar Searches.

Mozilla's thinking is that Firefox will never be fast enough, and this addon takes aim at improving the performance of your awesome bar. I didn't include this one in my three must-haves, but it's a close fourth now that I've spent some time using it. Coupled with my search bookmarks, this has become one of my favorite browser productivity boosters.

While there was an initial glitch that cause some excessive resource use, that has been addressed in more recent builds. The addon has been working very well on my two systems running Firefox 3.5b4.

If you're the daring type and always looking for new ways to speed up Firefox, give the Async addon a try.