Yes, thanks for the information. The more the feedback the better :)
The install problem is a bug in Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=855651 . Versions 21+ refuse to run extensions made with Iceweasel (rebranded Firefox), which I was using when I made mine via Mozilla's 'add-on builder' website. Further updates to Firefox should solve the problem.