It's been a while since I posted due to exams and whatnot. While I was out, Firefox got 2 major releases: 4 and 5. (5 is out in the repositories, so an update will get it for you) Currently Mozilla's plan is to release smaller updates much faster, so you don't have to wait half a year to get the latest technology.
The strength of this plan shows up when compared to a browser like Internet Explorer, which is only released every few years. It lags behind other browsers because it rarely gets updated. Firefox's new release schedule aims to overcome the delays Firefox experienced by getting the new updates out on a new "Major" release, which used to happen once or twice a year.
If you had the misfortune to use Firefox 4, I'm sure you'll agree it was quite a flop, especially on Ubuntu. The layout and GUI is clunky and slow and the browser uses excessive amounts of memory. Rather than waiting for FF5 to fix it, I took the opportunity to use Chrome/Chromium. I was thinking of using Chrome before, but didn't want to transfer everything from Firefox, however because FF4 effectively forced me to, I decided it would be worth it.
Chrome works well on Ubuntu, the only issue I have is the window decorations going out of Chrome's own fancy window, though I run it maximised usually, so it's generally not noticed. Chrome looks much more smooth than Firefox, even FF5 and has useful features like switching tabs by scrolling over them and a slick way of dragging a tab into a window. Not to mention it runs quickly.
When FF5 got released I downloaded the binary before it got into the main repositories and had a look. The GUI isn't much different from 4, but the browser itself is more stable and optimised. Firefox 5 generally uses slightly less memory then Chrome, but Chrome is slightly faster, so it's pretty neck and neck which to use. In the end I stuck with Chrome because I find it easier to use. After the Firefox 4 fail, FF5 is also an awesome browser that I find myself opening every now and again as well as Chrome.