hmm...well try scanning your computer(s) with virus scanners, ad-aware, and spybot search and destroy
links to get:
Spybot S&D ---
http://www.safer-networking.org/en/download/index.html) scroll down to find the DL link. yes it is free and yes it is safe. and no it is NOT illegal.
adaware ---
http://www.lavasoftusa.com/software/adaware/) same as spybot but for adware. very safe, very free, very legal.(note: this is SE not the personal(full) version but it works for getting rid of adware)
hope that helped :)
(note: yes i know you have been told to scan but you did not say that you had, and you only received the link to firefox, the safest browser ever.)
(another note: also try checking your "blocked web pages" list and make sure pcgm isnt on there)