There is no point and click way to do this. And there is nothing saying that it will retain all your settings.

You have to start by downloading the FF6 exe, then save all your Profiles - Where Firefox stores your bookmarks, passwords and other user data in a different directory(rename it old would work). Then remove FF, when you start up FF6 you would have to go to options and tell it not to upgrade, but be sure to do the updates they will be for security issues.

ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/6.0.2/win32/en-US/

This isn't working well. As directed, I first downloaded the Firefox 6 installer; backed up my profile; unistalled Firefox 7; and finally ran the Firefox 6 install. All this ran fine, but when I then tried to run the new Firefox 6 install it pops an alert dialog saying "Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system."

I couldn't find a Firefox process running in the task manager, and restarting didn't help; the same alert apears again when I try to launch again after the restart. I also tried unistalling and reinstalling Firefox 6 again (figured it couldn't hurt) with a restart in between, but the same thing happened again. I finally shut the system completely down (versus restarting) for about 5 minutes, but the problem once again presented after starting up again.

So, how do I get around this? Is this a known problem? Is there a process (perhaps running automatically at startup) I should kill manually to enable Firefox to launch?

"So, how do I get around this? Is this a known problem? Is there a process (perhaps running automatically at startup) I should kill manually to enable Firefox to launch?"

Known, I am not sure what you mean, if Firefox is running on startup it would have to be something you did. And what do you mean "I should kill manually" you said it was not in the running processes. I don't really know what you did but it has nothing to do with Firefox exe installing.
Did you remove both directories or just the Program File one?

It should have went like this...

1.Download the exe from the ftp site.
2.Backup any thing you wanted saved.
3.Remove from %appdata% the directory that FF data was in.
4.Remove the Program File directory FF was in.
5.Restart PC.
6.Find downloaded file and run it, allow FF to run and setup.

When I referred to killing an offending process manually, I meant finding it and terminating it in task manager; I was alluding to a notion I had (probably unfounded) that there might be some process other than Firefox.exe already running when Firefox tried to start, which it misinterpreted as being a running Firefox instance. Sorry I didn't make that clearer. Sounds like it's probably a red herring anyway.

Looking over your procedure list, it sounds like I may not have been rigorous enough in moving the old data where it couldn't be found (I basically just renamed the profile folder). When you ask whether I removed "both directories or just the Program File one," I'm not clear which two directories you mean; I know to manipulate the profiles directory (which resides under the Program Files hierarchy) - what's the other one?

I'm sorry to be such a trial, but I really do need to get this sorted by Monday morning if at all possible. Thanks for all the help!

On re-reading the above at the actual computer I'm trying to fix, I spotted what I missed removing the multiple directories. I tried again with the correct procedure and now have Firefox 6 up and running. (Sadly, my original problem with all the network errors is still there, but I think at this point I'll have to take advice in-house on that one.)

Thanks again!

Sorry it did not work out. I only gave you that because of your OP, myself I would have simply installed it with the new version as I have. I presently run 7, 8,9 and 10. I need the various versions for troubleshooting issues.

Good luck.