Are you sure it's spyware, rather than the standard browser pop-up, usually done with Javascript?
If it's spyware, (assuming you haven't done this) you may want to download, install, update & scan with Ad-Aware SE & Spybot Search & Destroy:
http://www.lavasoftusa.com/
http://www.safer-networking.org/en/index.html
If it's just some javascript crap, etc., getting by Firefox' pop-up blocker, you may want to investigate Proxomitron:
http://www.proxomitron.info/
I use it to filter (block) a wealth of garbage, including certain types of javascripts, ad banners, shockwave/flash, etc., etc. Surfing is faster, sites are cleaner, life is good.
I could definitely be misnaming the offending program...but it's not just a pop-up as it "popped up" several times over the past few nights and not just when I was at Hugh's site. I've run both of those programs and it didn't seem to fix the problem as well as I'd like.
For now, though, I'm going to avoid Hugh's site for a few days in hopes this gets fixed.
Oh, FWIW: Vonage has apparently had to plead and plead that it doesn't advertise with Spyware and the like (or that it doesn't fund it) so I know that, on some level at least, I'm not crazy.