Is this an infection? whats going on?

I was just using my computer when suddenly firefox popped up with a site that got blocked by avast. I wont list the link for obvious reasons but it looked like it was a link to a rogue installation site (e324rfds.rmicrodefender27)

I’ve also noticed that when I use google it gives me a message saying theres some kind of script thats making the page run very slow. Scanned with Avast and malwarebytes and it came up clean

What should I do?

Please follow this guide and attach requested logs: http://forum.avast.com/index.php?topic=53253.0

When done you will get help:)