Same problem here, I've managed to track the problem down to the Theme Font & Size changer extension in Firefox.
-- You received this message because you are subscribed to the Google Groups "Firebug" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/firebug. To view this discussion on the web visit https://groups.google.com/d/msgid/firebug/02dd621c-c64f-4bfe-8360-7247e7f03851%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
