You can return to an older version of Firefox:
Google - how to return to prior version of Firefox - - - you'll find numerous Mozilla Support web pages dealing with this topic.
Mozilla has warnings about going back to older versions:
1) "Important: By default, Firefox is set for automatic updates. To prevent Firefox from automatically updating itself after you install an older version, you'll need to change your Firefox update settings: Click the menu button
and choose Options. In the General panel, go to the
Firefox Updates section."
2) " Often when there is a problem with a Firefox update, people look for a way to go back to the previous version. That usually doesn't solve the problem and will make your computer and information vulnerable to attack. This article gives you some alternatives to downgrading and links to old versions of Firefox if you do choose to downgrade."
3)
"Warning: Using old versions of Firefox poses a significant security risk."
I copied and pasted the above quotes from one of the Mozilla Support websites. There's more, so I'd search the above topic before i returned to an older version.