Are you getting an error with a plugin-container file now?...
I got that. When I installed the Mozilla Firefox 3.6.15 upgrade, then restarted
the browser I ran Tools/Add-ons/Plugins/Find Updates also and got an error
in one of the add-ons... After that, every time I ran Firefox I got a Norton
anti-virus pop-up alert that suggested I should not allow the plugin-container
file to run because it was 'untested...'
Well, the problem seemed ominous but was actually fairly easy to fix. The
issue made simple is this error occurs whenever one of the add-ons isn't
working properly... The only problem is that it isn't obvious which one, so
what I had to do was disable one at a time, then restart Firefox and see
when the error went away.
In my case the error was with my Shockwave Flash installation... I disabled
and tested my browser by running a few frequently visited websites just to verify
this was the problem, then reinstalled the Adobe utility on my PC. Then I changed
this Firefox add-on status to enabled. And everything works fine again.
Good luck, hope this helps.