Where Can I Download Old Versions of FireFox
https://www.mozilla.org/en-US/firefox/all/
Download Past Versions
https://ftp.mozilla.org/pub/firefox/releases/
A Very Stable Enterprise ESR Version
https://ftp.mozilla.org/pub/firefox/releases/52.5.0esr/win64/en-US/
If you see this message: "Gah. Your Tab Just Crashed" You may need to use the ESR version.