High CPU use, close tab, it remains?

[FrankSMS]

I've noticed something I'm not sure is normal. Hopefully not. Using latest Firefox on updated Win7.
Sometimes on my slow computer certain websites use a lot of resources, often when playing hi-def videos. You'd think that once that tab has been closed the CPU use would return to normal. But I've noticed over and over....it doesn't. It remains just as high as before. Even for several minutes with everything closed and a blank tab open. Is this normal behavior for Firefox? Is there anything I can do? If I have many tabs open I do not want to close everything as it interrupts my work.

[therube]

It might not be abnormal for "high usage" to persist - even after a tab has closed - for a period of time.
Also possible that in addition to the particular tab that you have closed, other open tabs are causing high usage.

I have run into "miner" sites, where it may take a period of time before CPU usage drops, after closing the tab.
And I have been into sites where "usage" does not ramp up, immediately, as in they, purposely seemingly, do not start their mine from the get go, but instead wait for a period of time before initializing it.

[Brummelchen]

i repeat:

about:performance

then reload tab(s) and see result under "more".

[FrankSMS]

> Also possible that in addition to the particular tab that you have closed, other open tabs are causing high usage.

Nothing is visible on my desktop and Process Explorer shows no Firefox activity. Could something be running behind the scenes somewhere with Process Explorer not detecting it?

> I have run into "miner" sites, where it may take a period of time before CPU usage drops,

The last one that did this was CNN. I doubt they are getting into mining.