This question already has an answer here:
Sometimes there's a nasty, guilty, CPU-hogging tab in Firefox that's maxing one of my CPU cores and making the whole browser sluggish. I'd like to find it and close it.
Sometimes I get lucky, but not often enough. So even the slightest hint of which tabs are most active would be a great help. (That is, even without a Chrome-like process-per-tab model or 'Task Manager', any idea that a particular tab is over-active would be appreciated. Is it using a lot of JS timers? Triggering a lot of events/invalidations? Etc.)
Already have removed Flash. Already run with NoScript (which usually helps but occasionally, its partial blocking of a page seems to trigger the busy-loops). Fingering the top memory-users via the "about:memory" report is slow, awkward, and doesn't quickly find the real culprit.
So: is there any other developer feature that could help? Or an add-in? Or a third-party tool (perhaps based on attaching to FF like a debugger) that can 'blame' a tab for whatever pointless spinning is happening?
(Looking for a way to finger the tab or tabs most likely to be responsible. Not interested in solutions that require a Firefox restart each time the problem recurs: that already works but loses too much loaded data.)
(APPEAL FOR REOPEN: By being more specific about things tried and non-responsive answers, this highly-findable question can draw more directly-responsive answers, like the
about:performance answer hidden in @Thomee's comment and also at @fmt's answer on another question. Then as a true answer here, I could then 'accept' it for added findability. As it stands, the duplicate notice just points to yet another locked-as-duplicate question that also can't get the best current answer added/accepted.)