There are cases of google search links not actually going to the site you think it will be going to. The google search URL is specially crafted to go to a different and often malicious site. Given the firefox alert, avast alert and the other security site analyses, I believe the detection is good.
I think that this is what has happened here as I first checked out pcmech forum first (not via google searches) and no alerts.
Personally if it is something that I was looking for on pcmech I would do a search from within their forum, rather than from outside it (using google).
I'm surprised that firefox didn't throw up the alert I got for you, unless you haven't got the Block reported attack sites enabled.