Usually when you go to the tab and where the refresh button usually is there will be an [x] hit that and it will more than likely stop the annoying spinning.
Hope this helps,
i used to be able to disable/completely remove it from the tabs, but i cant seem to find a key to do it now. bump someone help me up please!
Discovered a solution, add this piece of code to userChrome.css file within a chrome directory in your firefox profile*:
/* Firefox userChrome.css */
list-style-image: url("chrome://mozapps/skin/places/defaultFavicon.png") !important;
/*if you have not got a chrome folder create manually both the folder and the file with exact names*/