* Open 11+ tabs with pages, images, etc. * Open the tabs tray. * Close the second tab. You'll see visible animation chop as the tiles reflow, even on a 6S. A user reported atrocious (fifty-second!) reflow with hundreds of tabs open, so don't stop at 11 if you want clearer symptoms. https://github.com/mozilla/firefox-ios/issues/1452 This might be just expensive animation, it might be computing a screenshot as a tab scrolls into the visible area, or we might be flushing the set of open tabs at the same time. Profiling should be enough to figure out what's going on.
tracking-fxios: ? → +
Ran the profiler with 28 tabs and wasn't able to notice a significant drop but there was a slight one. Looking at the profiler the culprit looks to be the preserveTabs invocation we make as a result of removing the tab. I also checked out the scrolling performance of the tab cell and noticed that we are adding/removing subviews every time a cell gets recycled (which is very bad considering we also instantiate a blur view as part of that). See attachments for the profiler outputs.
How much of the jank is fixed if we temporarily remove the call to preserveTabs?
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