I can still see quite-high CPU usage on this site (~100% of one CPU for at least 30 seconds after loading the site). A profile shows a whole bunch of youtube embedded videos being downloaded and a bunch of JS-engine time relating to that: https://share.firefox.dev/3id5pSp So I think this is unchanged. Having said that, comment 0 notes that Chrome is also-bad on this page, so there may not be too much of a discrepancy between us and them at this point. In any case, bug 1393977 would presumably still save some of our CPU time here.
Bug 1503620 Comment 8 Edit History
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I can still see quite-high CPU usage on this site (~100% of one CPU for at least 30 seconds after loading the site). A profile shows a whole bunch of youtube embedded videos being downloaded and a bunch of JS-engine time relating to that: https://share.firefox.dev/3id5pSp So I think this is unchanged (still a problem). Having said that, comment 0 notes that Chrome is also-bad on this page, so there may not be too much of a discrepancy between us and them at this point; this is just kind of a pathological site. Also, despite the high CPU usage, I don't notice any jank / interaction problems (though maybe that's just because I have a fast computer). In any case, bug 1393977 would presumably still save some of our CPU time here.