You can download and version ever made here https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/

1. Look though that list for the version you want. For example, 11.0
2. Pick a platform like win32
3. Then pick the language - en-US
4. You'll end up on a page with download links like this https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/11.0/win32/en-US/

Installing multiple older versions of Firefox could cause you a lot of grief when you switch to a different version from the last version you used. Firefox stores user data in what is called a "Profile"; using the same Profile for multiple versions is where problems can start.

There are a few ways to get around problems with the "Profile", but unless you are very proficient with software and can understand how Firefox Profiles work I wouldn't advise installing multiple regular versions of Firefox.

IMO, a better solution is to use multiple different versions of the Firefox Portable Edition, made by a 3rd party with permission from Mozilla.
http://sourceforge.net/projects/portableapps/files/Mozilla%20Firefox%2C%20Portable%20Ed./

Install the Portable Edition to your hard drive (or USB Flash device), the "Profiles thing" is handled by P.E.. P.E. creates its' own Profile in the folderset where P.E. is installed; it won't interact or affect any other Firefox P.E. installation or any regular Firefox installations.

PortableApps.com website
http://portableapps.com/apps/internet/firefox_portable

This site also might be useful: http://browsershots.org/

I constantly use different versions of Firefox. I have 4 of them installed at this moment and I use them with the same profile without issue.

If you want to install firefox and see how the pages look the-edmeister's reply is the safest.

But if you want to see how pages look without install firefox jscher2000 reply is just awesome.

hey jscher2000, where did you find this site (http://browsershots.org/ ) ?, just awesome, thanks a lot, it is very helpful for me.

thank you

Verdi,

That issue isn't as bad with the 4.0-Plus versions, or since Firefox 10.0 came out, but try that with a 3.6 version (or earlier version) and all hell can break loose. (The "owner" didn't specify which versions of Firefox he wanted to view his site in.) Of course, if the user doesn't have any extensions or themes installed about all the user will see is the "check for updates" routine for add-on compatibility, very little "damage" will be done. That message alone can be aggravating by itself, unless the user as a super-fast PC and they don't see that message for too long. (Like one second vs 5 seconds.)

I'd rather play it safe that have to help a user fix what that may have inadvertently broke. The Portable Edition creates the "roaming" folders directories (App Data and Local Settings) in a different location (in Program Files/Mozilla/Firefox/) than the official versions, so each installation gets its' own Profile and profiles.ini setup. No way one version is going to a different version's Profile, and cache.