I posted this 45 minutes ago, but don't see it on the forum. I have
added some additional info.
I have been running firebug for some time. I wanted to use it today
and see that is has disappeared. I have tried repeatedly to reinstall
it and it doesn't work. The only change that has happened recently is
an automatic update of firefox itself to the most recent version.
(3.0.10). I did not notice at the time if that created this problem,
but have not added any other extensions. Prior to the update I also
installed personas, but have removed that to see if it made a
difference, and it did not. Would like to know why it disappeared,
and why I can't reinstall in.
After further research I created a new profile and tried again. It
still would not install.