HELP! Firefox, Google, Avast Virus Warning

Ok, so, Firefox, Google and Avast are driving me insane!

Here's my problem:
Every time I use Google (regardless which way I search Google, ie. I type Google's URL into the URL bar or the Google search bar) Avast pops up and tells me that it just blocked a virus from Google.

Regardless what I search; even if I just go to the Google home page and various Google country sites (.com/.com.au/.co.uk etc) Avast always tellls me that it just protected me from a virus.

I have an updated version of Avast Free Anti Virus.
I ran it and it found nothing.
I ran CC Cleaner, cleared my cookies and history.
I ran Spy Bot and I got Rootkit Revealer and that didn't help either.

I emailed Avast and someone from the team emailed back and said that I needed to update Avast, restart my computer, rescan, get Spy Bot, get Rootkit blah blah blah!
They suggested all the things I had already tried.
Then they told me to go to a local repair shop.
Sigh!

BUT, I'm starting to think it's not a virus, or a cookie (mm cookies) or anything like that.
I think Avast is bringing up Google as a false positive.

I know Avast recommends using Google Chrome but as a university student, Firefox works best with my university provider and I am pretty stubborn.

The problem doesn't happen with other browsers, IE, Safari, Google Chrome.

I also deleted Firefox and reinstalled it and the problem still continues.

Can someone please help?