Sounds easy --- nope. I am using FF 3.0.10 (I know, old) and am quite happy with it. My computer is a 3.2g P4 with XP Pro and Update 3.
As I said, I am quite happy with this version and have very very few websites that won't work right. One of those, and the worst. is Google Maps. The page goes through it's loading and the map I want starts to appear. Then FF crashes with it's I'm sorry message. Some others, the layers don't line up but that's not a bad problem.
So back to which FF I should upgrade to, if any. I have my current version tweeked, tuned and set up just the way I like it and want all of that to carry over to the version that I may update to. Too many times. the buttons, the locations and the overall layout are changed in newer versions and that makes it hard to change what I am used to.
Last, can you install a newer version of FF as a separate program so that either FF version could be selected when I load a browser for my current use? Of course, only one or the other would be used. An example is that I can choose either my FF or IE8 from the desktop and can even have both running at the same time if I need to. That is how I use one of those layered pages that doesn't work quite right with FF.
Well, many thanks for reading, I'm looking forward to your thoughts. If you need any more information, just ask.