zlacker

>>mconle+(OP)
TL;DR: Windows Defender had a bug that made certain system calls expensive on CPU cycles when Defender's Real-time Protection feature is enabled. After discovery, Mozilla reported this issue to Microsoft. Microsoft is releasing a patch that should result in lower CPU usage when using Firefox on sites like YouTube (a ~75% CPU usage reduction was noted when browsing YouTube in Firefox with the fixed version of Defender).

It seems like the HN submission form truncated the # from the end of the URL I linked to, which linked to the relevant comment. I'll try that here:

https://bugzilla.mozilla.org/show_bug.cgi?id=1441918#c82

and

https://bugzilla.mozilla.org/show_bug.cgi?id=1441918#c91

>>mconle+h3
I've seen some really weird performance behavior from Defender and I just keep it disabled on my desktop device now. I'm not surprised to see it affecting Firefox like this. Defender's dropped all the way to the bottom of the list in effectiveness anyway, so I don't feel it's a big loss.