I did the suggested cleaning out of cookies, etc. on my pc this afternoon and it really did speed things up. Still slower than it used to be but not so excessively so now.
I cleaned out both my Outlook and my Firefox caches. If you haven't done so, it is worth trying. With Firefox, you click On "Tools" then look for the option of "clear recent history" and click on that. In Outlook, it is called "Delete Browsing History" (It is the first option under Tools on my pc).