A couple of days ago, Firefox managed to disable everybody's add-ons - an expired certificate, or something.
Oops.
Apparently, the newly released version 66.0.4 resolves the problem.
It doesn't seem to have found its way into the Ubuntu/Mint repositories yet. This workaround got my add-ons working:
about:config (in the address bar - then press Enter);
Click through the warning;
Look for this entry: xpinstall.signatures.required (Simply type it into the bar which you'll see above the list of configuration entries)
and double click on it to toggle it from True to False.
Next trick will be remembering to set it back to True once everything has been sorted out...
Meantime, grateful thanks to the folk who posted that fix on various places in the internet.
If you're using Windows or otherwise install your Firefox "manually," then simply updating to version 66.0.4 should resolve the annoyance with no need for workarounds.
