[Webkit-unassigned] [Bug 218704] New: Safari Web Extension: Browser action popover with height >=441px glitches

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=218704

            Bug ID: 218704
           Summary: Safari Web Extension: Browser action popover with
                    height >=441px glitches
           Product: WebKit
           Version: Safari 14
          Hardware: Macintosh
                OS: All
            Status: NEW
          Severity: Critical
          Priority: P2
         Component: Layout and Rendering
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: winlinx at ya.ru
                CC: bfulgham at webkit.org, simon.fraser at apple.com,
                    zalan at apple.com

Created attachment 413580

  --> https://bugs.webkit.org/attachment.cgi?id=413580&action=review

Reproducable Xcode project

Safari Web Extension in Safari 14:

Elements in the bottom of big popover (>=441px height) behave strange. For example when I hover on such element the focus style and cursor constantly blink, it seems as if I move mouse really fast over element up down.

This not happen for elements located before this threshold (above 441px height).

Check video https://share.getcloudapp.com/qGuvddqj . I also attached reproducable Xcode project.

I also noticed that something strange happening with layout recalculation in browser_action popovers. When you try to use libraries like react-textarea-autosize (auto resize textarea elements) - they work really slow, especially if you have more than one on a page. If I check Performance tab in Developer tools there 46% and 43% of processing time spend on Layout and Styles respectively.

I suppose hover behaviour and layout recalculation problems I mentioned have something in common, so I decided to put them in one ticket.

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