I have reformatted and reinstalled everything a-new. (Other issues)

Played with auto updates and disabled them. (Made no difference)

Disabled/uninstalled all other add on plugins. (Made no difference)

Just as bad on Chrome - It has always been misbehaving like Firefox is now.

First thing I tried.

After firefox big update around October 2017

Reformatted the whole thing and still happening.

The same is going on for me on Chrome and Firefox. It is a shame because it is the best ad on and I have been using it for years. 2008 Mac Pro, 10.11.6.