I can give you my experience:
I have installed and uninstalled multiple versions of Mozilla and now Firefox over the years. I have never had a problem. [Unfortunately, MS's latest hotfix has messed up my IE6--grrr-- it hangs now.]
I can't think of a reason to fear using Firefox. Yes, I do believe it's superior to IE6. Set it up. Import your IE6 bookmarks. Try out some of the extensions. [This Bugmenot extension is wonderful.] Let me know if you have a question that I can help with.
Ok....I have been playing with it the last hour or so. (using it on this post, in fact)
Love the Bookmark Manager. (FR and Drudge etc. a quick snap away)
How do you get the little Google bar in the right corner to work?
I have "Google Search" and the "Google Toolbar" loaded on my IE6
Can that be installed into/onto Firefox?
(Hope you don't mind me asking these questions, but the Firefox "Help" and FAQ don't seem to be a lot of help)