Removing Firefox Mate screen from Ubuntu Mate
Solution 1:
I got my answer on Ubuntu MATE Community.
As Norbert_X (Popularly known as N0rbert on Ask Ubuntu) said in his reply to my thread :
You can override such behavior by removing two files using terminal commands:
sudo rm -v /usr/lib/firefox/ubuntumate.cfg /usr/lib/firefox/defaults/pref/all-ubuntumate.jsand then restart Firefox.
Please note, that we do not pin/lock theubuntu-mate-default-settingscorresponding package version, so you should apply the above fix again when Ubuntu MATE 22.04 LTS will be released.