On some sites, the CPU usage goes to 100% (one core) and it freezes any activity inside the browser. For example I can move the window, but not click the tabs or in the page, and if I do, the actions are delayed.

One site in particular, izismile.com, can make this 100% usage to go for tens of seconds, even a minute or so. The network activity doesn't seem high, a few KB (LAN included), so I thought maybe it struggles with communicating with relays, but sometimes it is possible to have a few seconds break, during which if I open up other sites, tor.se for example, they open up fast, no glitches.

Why is this happening and should I worry? I am using the latest Tor Borwser (9.5) on Archlinux x64, with javascript disabled, no tracking, some extra about:config changes, all coming from privacytools.io. Also uBlock Origin, the only foreign thing added.

  • Maybe these sites are using your coputer in order to gain some computing power from you. Some use their visitors’ machines to calculate hashes for cryptocurrencies or something similar.
    – Nemgathos
    Commented Jun 21, 2020 at 17:34
  • @Nemgathos This also occured to me, but when I fire up top or ps axw, the only processes that might show 100% usage are Browser/firefox.real, or Web Content, which seems just another name for Browser/firefox.real -contentproc -childID 1 -isForBrowser -prefsLen 1 -prefMa (for example). Would these two be used behind the scene for cryptocurrency-related activity? Also, this only lasts 10s of sec, then everything goes back to normal. It might happen again when opening up a link in their page, sometime in the future, might not, but in rest, everything seems fine. Still, I had to ask. Commented Jun 21, 2020 at 17:56
  • I don’t know whether this is the case or not. I suppose that it just lasts for a short while because the site operators want you to come back and not feel “abused”. But maybe, the reason for all of this is something else that we do not have in mind.
    – Nemgathos
    Commented Jun 21, 2020 at 18:09
  • @Nemgathos I don't know what to think, this isn't consistent. Sometimes it goes smooth, sometimes not. I'm just as confused. Commented Jun 22, 2020 at 11:31

1 Answer 1


I can't be sure of this, but maybe it's a workaround, after all. A few times I noticed that the page was waiting after facebook.com, so I added an entry in uBlock Origin, and since a few days ago, it seems to behave. I posted this as an answer because it seems to have an effect. Whether it is so, or not, I don't know.

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