I think I was able to reproduce this on my Macbook. I captured some profiles: With close button: https://share.firefox.dev/44krQLR With close button hidden: https://share.firefox.dev/44jpvAN It looks like with the close button, we're doing main thread fallback painting... and it gets a lot more expensive for some reason. Hey mstange, any idea why [this change](https://phabricator.services.mozilla.com/D176920) would cause painting while scrolling the tab manager panel to become so expensive?
Bug 1839037 Comment 3 Edit History
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I think I was able to reproduce this on my Macbook. I captured some profiles: With close button: https://share.firefox.dev/44krQLR With close button hidden: https://share.firefox.dev/44jpvAN It looks like in both cases we're doing main thread fallback painting... and it gets a lot more expensive for some reason with the close button visible. Hey mstange, any idea why [this change](https://phabricator.services.mozilla.com/D176920) would cause painting while scrolling the tab manager panel to become so expensive?