Why is the slowest tab usually a blog post that I've had open in a tab for a week without looking at it? (from Firefox about:performance)

Feb 11, 2017 · 10:21 PM UTC

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In this case, spending most time in a setInterval that's just reading document.cookie, described in logging as "IDP Session Cookie monitor"
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Though I managed to crash my entire system with out of memory before I figured out how big document.cookie was...
Replying to @fwenzel
Well, I did have to switch it to the foreground to profile it. But the initial screenshot was when in the background.
Replying to @fwenzel
For the record, I recorded this problem at github.com/webcompat/web-bug…
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