I often open links in new tabs and come back to them later without noticing that it never quits loading so this may be handy.
I installed it this morning and it has kicked in a couple times.
“Some pages will not finish loading because of internal problems or the use of ad-blockers and other filtering tools.
This extension stops pages from loading indefinitely and slowing the browser.”
Address : addons.mozilla.org/en-US/firefox/addon/killspinners/