There is not enough information here for a theory, but could it be the packaging/installation process causing this?
Knock wood, I have not seen this problem with any version of Firefox that I have used (now 68.0.2; not ESR). I get the 64-bit package directly from Mozilla and untar after verifying the signature. It is easy to return to the old version if I have an issue.
I do delete the “features” that Mozilla seems to think I need.
I installed uBlock Origin as an add-on long ago. I use ‘strict’ blocking.