One of the problems that befell (almost all) Firefox users, midnight from May 3 to May 4, 2019, was, that many extensions which we had installed had suddenly become deactivated because an Intermediate Certificate used to sign those extensions, had simply expired. Apparently, somebody overlooked that status of the certificate in question.
To remedy this situation as quickly as possible, Mozilla offered to publish a “Study”, which is a kind of project that Firefox users can subscribe to, and the purpose of which usually is, to allow Mozilla to conduct experiments on users’ browsers. This study had as purpose however, just to install a renewed certificate.
One important piece of advice is, ‘If you are still experiencing this issue, Do not try to uninstall and reinstall the extensions. Doing so would delete all the data stored with the extensions, while simply to have them disabled, and then to have them re-enabled, will allow most extensions to keep their stored data!’
Therefore, to receive this fix, what Firefox users were advised to do, was to go into ‘Tools -> Preferences -> Privacy & Security’, and there, to Enable Studies. The problem which I experienced myself was, that this advice was not narrowed enough, for Linux users with ‘Firefox ESR’. First of all, the Linux versions of Firefox have their Preferences sub-menu under ‘Edit’, not under ‘Tools’, but that was the least significant problem. What was worse was that, under my Linux distribution, the option we were advised to check was greyed out, and could not be checked:
(Edit 5/10/2019, 22h10 : )
Because as of this time, under Debian / Jessie as well as under Debian / Stretch, the official fix for this problem has been pushed through the package repositories, it’s no longer advisable by any means to apply the workaround described here. However, the update under Debian / Stretch was a bit slow in coming, for which reason this workaround served me well.
(End of Edit.)
However, I was able to get this feature of Firefox ESR to work anyway. And what follows is how I did that…
(Updated 5/06/2019, 16h00 … )