0569
Firefox 76 forces a huge address bar upon users
If using the bookmarks toolbar, this can be a nuisance, since the bookmark titles get covered by a shadow, especially whereas this even happens right after startup of the webbrowser. This can only be
disabled relatively easily using 'about:config' in Firefox <77. In later versions, userChrome.css has to be tinkered with.

This can force the user to resort to external cloud solutions, such as a Google Chrome-account, for sharing bookmarks inbetween several computers, rather than safely handling this privately. Since October 2019 this even applies to Firefox ESR.
The
Livemarks-plugin provides a reasonable alternative, though it would be nice if fully automatic migration could be offered, preventing the kind of steep learning curve of finding the "Options" screen belonging to this specific add-on in order to import the OPML-file exported by the Firefox-installer, especially since the "Options"-menu option disappears on Firefox-installations that permanently run in in-private mode and because the "Import"-file selection screen does not offer an "*.opml" file filter pattern.



Keeps obsoleting older plugins, prohibiting use of JS Print Setup on Firefox 57 (Quantum)
Pale Moon (safest choice due to continued updates) together with manual .xpi-addon installation, or Firefox Extended Support Release (
ESR)
V52.7.3 can be used to avoid this, while disabling automatic updates for Firefox and for add-ons, at the expense of exposing security risks. It should be technically possible for the Firefox developers to let the user choose to keep using the many older SDK plugins, at a cost of performance loss.
Another solution could be to use the semifree/semicommercial operating-system-based QZ Tray printing software, that can communicate with the webbrowser through Java, at the expense of a couple of additional programmering hours. While this will avoid Firefox-addons altogether, it introduces a Java dependency and it risks small differences between what's the screen content in Firefox as compared to the printed results, depending on whether the direct-HTML or pixel-capture technique would be used.

Installing add-on from .xpi-file in Firefox 52.7.3 ESR or Pale Moon