Screen recording:
2019-09-07 10:02.mp4
Environment
root@momh167-gjp4-8570p:~ # date ; uname -v
Sat Sep 7 10:39:13 BST 2019
FreeBSD 13.0-CURRENT r351708 GENERIC-NODEBUG
root@momh167-gjp4-8570p:~ # pkg query '%o %v %R' firefox
www/firefox 69.0,1 FreeBSD
root@momh167-gjp4-8570p:~ #
Thoughts
The effectiveness of extensions such as Malwarebytes Browser Guard might be limited – in Firefox and the like – by this Mozilla bug:
1378459 - (webextensions-startup) [meta] Allow some addon functionality to load prior to any content loading
From https://bugzilla.mozilla.org/show_bug.cgi?id=1378459#c51: