You should be able to use the current release version, Firefox 3.6.13

http://www.mozilla.com/en-US/firefox/system-requirements.html

You can use the current version which is Firefox 3.6.13. You can also use Firefox 4 which is currently in Beta development.

dear TonyE and Swapsomething, if you are running old versions of Windows, the last FF version which can be used is FF 3.0.19,

I have two computers: 1) running Windows 7: FF 3.6.13 works fine and I like it very much 2) running Windows XP: FF 3.6.13 does not work on it (you see the scrollbar on the left side of the screen, you cannot use your bookmarks, links do not work, the only way to reach a page is to type the address, and so on for every other page). On this computer I use FF 3.0.19, which now is about two week that hangs quite often, and cannot even upload my add-on on the Mozilla website.

p67543, you are absolutely incorrect. If you talk about Windows XP, I am siiting in front of a Windows XP computer and typing this reply to you using Firefox 4 Beta 12. Windows 2000 is also supported both by Firefox 3.6.14 and Firefox 4.0 Beta 12.

Yep, Firefox 3.6.x versions are fully supported on W2K. But, Firefox 4.0 will be to a lesser degree, not fully supported but the installer won't disallow installation on W2K or WinXP SP1. Down the road with 4.0.point releases the Mozilla developers won't purposely break anything with regards to supporting W2K, but if a new feature wouldn't work with W2k or WinXP SP1 that could be the end of compatibility.

Yes, Windows 2000 and Windows XP are currently supported. For the ones who are facing difficulties using Firefox 3.6 or Firefox 4.0 on Windows 2000 or XP -

Windows 2000 users - Ensure Windows 2000 Service Pack 4 is installed.

Windows XP users - Ensure that Windows XP Service Pack 3 is installed.

Installing the latest service pack AVAILABLE is a solution to many problems as service packs contain large amount of hot-fixes and error-fixes.

I'm currently running windows 2000 professional with Firefox 6.0. You or this web site tells me that I should be using Firefox 3.6.13 . My question is - Can I install Firefox 3.6.13 over Firefox 6.0? I also have another problem and that's when you started telling me that Firefox 6.0 is available for download and I do not down load it, you automatically download the program when I start up my computer and I feel that is wrong. I should be allowed to say NO, I do not want the newer software.

@hatsoff,

Welcome,

"I should be allowed to say NO, I do not want the newer software."

The option is there. Go to Firefox button (to display Firefox button on Windows XP and 2000, right click the tab bar and uncheck Menu Bar), now click Options. In Options, click Advanced tab. UNDER Advanced tab click the Update tab. Under "Automatically check for updates to" uncheck Firefox and under "When updates to Firefox are found" select "Ask me what I want to do". DONE.