content: If you have the regular build (not the nightly/dev one) then the xpinstall.signatures.required set to false doesn't fix this. But I got all of my add-ons back by going to about:debugging. Check the box to enable add-on debugging. Then click Load Temporary Add-On. Browse to your Firefox profile in appdata: C:\Users<Username>\AppData\Roaming\Mozilla\Firefox\Profiles<some random shit>.default\extensions In the extensions f  136d  older there are .xpi files, those are your extensions that you had. Load each one and don't close Firefox until they fix this.