Well for MONTHS I have been struggling with my work computer, it's a high spec unit, and after a few days it would get laggy and horrible. I tried everything I could think of, and could finally narrow it down to when firefox was running. Perfmon would say everything was pretty normal, but it was definately not. In the end I gave up and uninstalled Firefox, and low and behold my PC was a new beast, I had migrated to Chrome (Much faster regardless), and soon I noticed my PC gettting (a little less) laggy again. 

Turns out the problem all along was the skype plugin, which when removed made both browsers happy again and I feel like I just got a massive computing speed upgrade! It's now on my install blacklist!

I hadn't been having problems at home, but removed the skype plugin and now my home computer feels like it's massively much faster too!