Hello,

this doesn't appear to be a default Firefox message. Please see if this helps you: Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

Next thing I'd therefore try is the Safe Mode: Diagnose Firefox issues using Troubleshoot Mode.

Cheers! --Tobbi

Tobbi,

Thanks for the link for resolving my problem. The problem was with one of the add-ons. It was the toolbar that I thought I had deleted, but found that it was still active in the add-on list. Deactivating it solved the problem. I had since deleted it.

Roger

rogerdstx,

It would be helpful if you would indicate the name of the toolbar which was the source of the problem! It seems every program I download wants to download a toolbar and goodness knows what else. Sometimes they do so without even asking, I think. Mostly they have tabs for facebook, twitter, and many other items I do not want. I think we have a right to know what program (s) produce the error message "an unknown change" quoted in full in the original message. Perhaps if we knew, the offenders could be persuaded to mend their ways. Otherwise we can expect a further dozen messages or more per week saying "I have this problem, too"

rogerpb