The first and best Ad-blocker out there. xD

The newest version can be installed on a old version of Firefox (using version 56 myself) by going to this url: https://bugzilla.mozilla.org/show_bug.cgi?id=1549017

Follow the instruction written on the 3rd and 5th comment. 3rd:

"Full Procedure:

Go to about:support in the URL bar.
Open your profile directory.".....

5th comment:

I prefer the temporary fix that I outlined here:

https://www.reddit.com/r/firefox/comments/bkcjoa/all_of_my_addons_got_disabled_and_they_are_all/emggvbx/

A temporary workaround:...

Thanks the ones with the ideas, not me. :)