Where can i download old versions of Firefox?

I need to download old versions of Firefox (version 6, 7 and 8). Does anyone know where I can find those?

I’d have a look at mozilla.org

You can find them here https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/
source:- Install an older version of Firefox | Firefox Help

Why do you want old versions with known security vulnerabilities?

Security Advisories for Firefox

Thank you for the direct link!

I have customers on old browsers (they cannot switch) and I need to make sure everything works in those old versions.

you are welcome