I re-enabled mine by setting Add in debugging on, and loading the xpi files from %Users%\\Appdata\Roaming\Mozilla\Firefox\Profiles\.default\extensions
It should put all the 'working yesterday' Add ins into the temporary extensions while FF remains open, repeat if needed.
*Carefully check that you have those which you expect, and none that you don't* then continue browsing till Mozilla get their act together - this is the second time in 3 years they've dropped the ball on this.