I'm sure this isn't a server issue Tony.
It could be a simple case of the PCs being taken over by viruses. Some of them do things with your Name Service (replace the resolver) and that can cause things sometimes to appear very slow when the PC is looking for IP addresses and doesn't find them.
It could be that the browsers which are giving problems are running on machines which aren't powerful enough to do everything that they're being asked to do all at once. At least one poster said that he had other tabs open at the same time, and that's the sort of place where I'd start looking.
As well as other browser tabs, try stopping everythng else (well, as much as you reasonably can) that the computer is doing. Things like mail clients, dopey Acrobat 'speedups' and other startup junk, maybe even your anti-virus -- basically anything that's using computer resources.
If you're using Windows check the task manager for unwanted processes. If it's Linux or a Mac use 'top' or similar -- but then you probably wouldn't have a problem anyway.
There are a couple of packages that are very useful for checking Windows boxes:
MBAM:
http://www.malwarebytes.org/products/malwarebytes_pro/
CCleaner:
http://www.piriform.com/
Don't ever download anything from CNET.com, no matter what they tell you.