Amazonaws causing problems with Firefox

[Malevolence]

Does anyone know what this crap is?

I don't know which site it is as it happens on quite a few, Imgur, digitalspy.co.uk and Wikipedia are two culprits, this thing starts my connection uploading/downloading causing Firefox to lock up and unable to open any more websites. Hell, it won't even allow me to refresh any sites already open in tabs. The only way to fix it is to close Firefox and re-open it.

I'm not running anything on my system that causes this and I've run both AV and anti-malware scans which have all come up as negative. So it has to be something on these websites that's causing this to start. I've tried adding ec2.amazonaws.com to my HOSTS file but it still persists. Is it some sort of Amazon CDN or something?

Is there anyway to block this thing?

 

[Malevolence]

Tried Firefox in safemode with no luck. Switched to Waterfox and, touch wood, all seems to be fine. I read somewhere that is it maybe some of Firefox's new 'features' that cause this, the main culprit could be the 'Sync' feature they added a few releases back.