Well here are few suggestions including few of which I have already posted:
https://support.mozilla.org/en-US/questions/981141
I really can't remember how I solved my issue in the end. If nothing
described there works, the problem might be in the Firefox itself. In that
case you may just wait for a new Abrowser release. If you decide to reinstall
Abrowser, you should purge it instead of just removing it. Use:
sudo apt-get purge abrowser
sudo apt-get install abrowser
You may also check if the preferences folder was removed and delete it
manually if it persists after purging Abrowser before installing it again.
