That's not a "cookie", it's a Javascript error message caused by something wrong with the Skype extension for Firefox. Open the Add-0n Manager Tab - {Ctrl + Shft + A} - and disable the Skype extension. Skype needs to fix that problem; check with them to see if they have an updated, fixed version of that extension available for their users.

Bless you. It worked. Under "Extensions" it mentioned that Skype extension is incompatible with Firefox 5.0. I've disabled, and like you said, I've written to Skype. Thanks so much. "Rudy"

I noticed that a few people said the problem was the Skype extension. It cannot be Skype if you have Mozilla Firefox 5 because the Skype extension is already disabled and doesn't work in Firefox 5. I found that when I entered the error message verbatim into search engines, entries kept cropping up for Integrated Gmail add on. I disabled that, and it seemed to fix the problem. Hopefully the Firefox and Gmail people will fix it soon, so I can turn Integrated Gmail back on.