FF3 Hack - http://planetzarg.blogspot.com Rated 5 out of 5 stars
It seems likely this is an abandoned add-on. Which if that is the case it is a TRUE shame. The FF3 hack posted below works. Might take a little doing but the principle instructions are sound. I can use FF3 now. ;)
Also I just used 3.* instead of 3.0.0.* to hopefully allow functionality through more updates. Not sure if that will actually do that but it worked. ;~)
I do hope for a proper "supported" version though. Who knows what/when update of FF will break this hack.
Also.. http://www.phraseexpress.com is a pretty interesting alternative. Its basically a 10x more function OS counterpart. It will require a re-adjustment in operational dynamics to work with browser work.
I'm sticking with my hacked signature add-on for now though! I hope someone maybe takes this over or writes a new one so additional features can be added etc.
Yes, thank you miek for what you have given us at least to start with!