am trying to figure out why firefox is preventing my iMac from sleeping. according to activity montior, it shows that firefox is the reason why my iMac wouldn't sleep. I have only one extension (pearl crescent page saver) that I had been using for a long time. and had been updated to latest version. my iMac had gone to sleep previously with that extension. I have 3 plug ins - openH264 video codec, shockwave flash and widevine content decryption module by google. hmmm?