Firefox 43: Disable check for "unverified" add-ons

This is a bit of a temporary fix because it won't work for Firefox 44, but for the time being you can simply change a setting in your config editor.

• Open up a new tab and go to "about:config"
• Paste in xpinstall.signatures.required and set it to false

Restart the browser so the disabled addons are re-enabled.

I'll update this post with methods to self-sign the addons once Open Live Writer is patched to work with Blogger's OAuth2 sign-in API.

Source 

• Using "unverified" add-ons | Firefox Support Forum | Mozilla Support