Is the program itself running slow in general? When you look at the resources used, is it using a lot of memory?
It sounds like there is something which is making the browser use a lot of resources - you may be better to create a new (blank) profile, and then copy your bookmarks across and reinstall any extensions.
My Firefox browser uses Min 250KB memory. I know this is very high. I have two extensions disabled which are not compatible with FF 22.214.171.124. Could this be dragging it down? Is there a way of measuring how much memory each extension uses or is it just the case of finding out the name of the process?
Will look at creating a new profile - thanks for the tip.
I've established since my previous post that the lag is caused by a VPN, which I am being forced to log into to receive emails...