If you are encountering this bug, please see Comment 5 first for the information that would be helpful for debugging and fixing it. There are also some known workarounds: - If you are seeing the error 0x805a1f65 in the Browser Console and you have a Master Password, then resetting your Master Password may fix it (see https://support.mozilla.org/en-US/kb/add-ons-disabled-or-fail-to-install-firefox#w_master-password) - If you are seeing the error 0x805a1fe8 in the Browser Console, then changing file permissions for certain files in the profile directory may fix it (see Comment 35)