The issue, he wrote, is that Chrome doesn't return the system's processor to an idle state when it's not doing anything. Instead, Chrome sets a high “system clock tick rate” of 1 millisecond, and leaves it at that rate, even if the browser's just running the background.
I wouldn't doubt it with a modern browser.
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They could also do some form of memory flushing, etc., because some extensions/add-ons are heavy on RAM usage (I'm looking at you Adblock for Chrome) and bloat Chromium-based browsers more than a default installation.