If you can't find a mudcat cookie, it's probably because you're not getting a persistent mudcat cookie.

I'm afraid I agree with that!

blocker/popup blocker, perhaps via a Firefox plugin? The add-in,

Firefox uses "add-ins," I think that's the same thing. Only one I've accepted is RealPlayer.

I've set its pop-up blocker to Notify me with only 5 Allow exceptions (like my bank!) Does Mudcat use pop-ups to set cookies?

Firefox doesn't use security zones...one of the reasons I prefer it.

No Toolbars in the usual sense. Just a search preference option that includes Google & several others.

Hmm. Now you got me thinking. I wonder if Ad-Watch could be doing it. It can be annoying and unpredictable but it's saved my bacon any number of times. It lets me set other cookies...

I'm sure (pretty sure) Symantic AV wouldn't do that. I have it running live time (Auto-protect) and do a Quick Scan daily at lunch time. It caught two nasties just this week after two-months of peace.