How to get multiple versions of the same internet browser?

[yourofl10]

I have one question, I run FireFox on my computer but how do I get different versions to run? IE: I can have FireFox 3.0 and FireFox 3.1 running at the same time. But how do I get 3.1 (for example) on my computer but still have the old version on my computer. I like keeping older versions of stuff on my compiter just in case if the new version I dont like.

Thanks!

[Kamazar]

I guess you could download one copy, and when an update comes out for it, instead of downloading it, download a new copy from the main web site and rename the file so that it doesn't overwrite the old one.