No longer works with Firefox 43 because add-on is unsigned.

[bulrush15]

Can you get this add-on signed? Firefox 43 now no longer allows any unsigned addons at all. FF disables all unsigned addons with no way to enable them.

[antoyo]

The add-on on the Mozilla Add-ons website is automatically signed. I was able to install it in Firefox 44.

If it does not work for you, one way to install it is disabling add-on signature:

• Enter the url about:config in Firefox.
• Search for xpinstall.signatures.required.
• Set this setting to false.

If you prefer installing only signed add-ons, you should ask Mozilla about this issue since this add-on is signed and I cannot do anything to help you since the signature process is done by Mozilla.

[Gitoffthelawn]

I can confirm the extension on AMO is properly signed.