Have you contacted their support or checked for updates?

Install an older version of Firefox {web link} Look for the directory of the version that you want. But remember that old versions may have security issues.

https://www.trusteer.com/en/support/supported-platforms https://www.trusteer.com/en/support/how-can-i-tell-rapport-working

Firefox Version 50 Support Firefox version 50 is not currently supported. We apologize for any inconvenience this may cause...

So you will have to wait for a update from them.

Firefox is not made to support the hundreds of extensions but the other way.

Deleted  (same answer posted by James)