I'm currently in the middle of testing some UI work that's been done on a project I'm working on. This is the type of testing that many of us love to hate. The goal: find all the styling errors that remain after this "UI cleanup". I have five browsers to support (IE 6 and 7, Firefox 2, and Safari 2 and 3).
So how to best go about this?
This is one of those things that to me you just have to dig in and do it manually, at least the first time. This type of layout and front-end styling is extremely tweaky across browsers (pity the guy who had to code it!). Also, you have to experiment with how it handles data across your constraints, from no value to the longest allowed value. Still, that being said, this can be BORING testing.
I try to see this kind of test as an opportunity to get acquainted with the app again as a user sees it. A lot of the time we're deep in the guts of the app, checking boundary conditions, exercising deployment constraints, testing and verifying a limited portion of the app, doing configuration tests, testing behind the UI. This is our chance to use the app as the user sees it.
So embrace the manual test, reacquaint yourself with the feel of the app as a whole. You'll probably find more than styling issues!