Determine which tab in Firefox is using CPU resources?

Is there anything in the current Firefox similar to the Task Manager in Google Chrome? (Shift + Esc)

There is something that occasionally takes up enough CPU to make Firefox unresponsive - but with multiple windows, each with a dozen or so tabs open, trial & error is going to take a while.

Solution 1:

Resource usage can be monitored via the about:performance page which goes as Task Manager since Firefox 64. It had a major overhaul and now gives much more detailed insight into the performance of tabs and add-ons.

Solution 2:

about:memory shows Firefox's memory usage details. There's also a button on that page that allows you to minimize memory usage.

Solution 3:

The first likely culprit is Flash. Kill Flash - now.

Then it may be rogue Javascript code. Firefox's Javascript Deobfuscator extention lets you watch the count of Javascript function calls :

It is not a measure of CPU usage, but a close enough proxy : find the function with a runwaway number of calls and you will likely have caught the culprit.

Solution 4:

Firefox 16 should introduce proper built-in profiler at last.

Solution 5:

By using Flashblock and Nevercrash, now replaced with FlashStopper and UnloadTab you go a long way into blocking Flash or tabs, preventing CPU waste instead of tracking it. This holds, but less, for memory too. Flash, e.g. Youtube is prevented to start until you click on them, so you may launch them in several tabs and they wait for you to open the tabs. Tabs are uloaded from memory and idle until you reopen them and they are refreshed from the cache (if still available).
Shutting down the Internet for a while also works during the time you don't need it ;-)
Firefox fragments virtual memory so much that it's using an excessive amount of real memory (there is too much unused virtual memory in real memory). One needs to periodically stop and restart Firefox with the same pages. That will defragment its memory and the whole system will run faster by reducing the swapping.
On my Ubuntu system, real memory usage slowly climbs up to 98%. Then it's time to stop Firefox and restart it: it will then use less than 1MB of real memory instead of 3MB. The same holds for Thunderbird..