I can reproduce this in Nightly on Windows 10, too, FWIW. (We had some reports in the QF triage meeting that folks on non-linux platforms were having trouble reproducing, but now I'm wondering if perhaps they were just watching for the repaint [which happens quickly] rather than for the page to continue to be interactive e.g. for clicks to change blinking cursor position -- that's the easiest way I've been able to determine that the content process is hanging here without editing the document.)
Bug 1524334 Comment 6 Edit History
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I can reproduce this in Nightly on Windows 10, too, FWIW. (We had some reports in the QF triage meeting that folks on non-linux platforms were having trouble reproducing, but now I'm wondering if perhaps they were just watching for the repaint [which happens quickly], rather than watching for the page to continue to be interactive, e.g. to respond appropriately to clicks that should change the blinking cursor's position. That's the easiest way I've been able to determine that the content process is hanging here, without editing the document.)