NoSquint Plus (originally NoSquint) was a favorite add-on - until the three very convenient and intuitive adjustment buttons were removed; I had been using version 56.1 in Firefox ESR (now at version 52.6.0) until it was apparently disabled.

Why was NoSquint 56 disabled?

In any case, it has now been removed and replaced with Zoom Page (version 15.8), which is merely adequate.

What had been an outstanding add-on has been destroyed; what a pity.