STR: 1. Ensure you have "Bookmarks toolbar: only show on new tab" (this is the default) 2. Open two tabs, side-by-side. The first tab should be `about:home` (the new-tab page), and the second tab should be the attached testcase. 3. Switch back and forth between the two tabs. ACTUAL RESULTS: Every time you switch to the testcase, you can see that it's logged to indicate that its viewport changed height. (This is from the toolbar appearing and/or disappearing while that tab is focused.) EXPECTED RESULTS: The toolbar-hiding-behavior should not cause the viewport of the testcase to change height. Conceptually, the toolbar should only be present for the new-tab page; the testcase shouldn't incur layout-jank as a result of that toolbar being hidden from the tab-switch operation. I ran into this "in the wild" at Google Photos -- I was viewing a large photo which is scaled to fit my viewport, and I noticed that there was a visible "jump" in the photo rendering whenever I switched from a new-tab to the Google Photos tab. (It would briefly render at the smaller toolbar-smooshed size, and then render at the full viewport size.)
Bug 1705215 Comment 0 Edit History
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STR: 1. Ensure you have "Bookmarks toolbar: only show on new tab" (this is the default) 2. Open two tabs, side-by-side. The first tab should be `about:home` (the new-tab page), and the second tab should be the attached testcase. 3. Switch back and forth between the two tabs. ACTUAL RESULTS: Every time you switch to the testcase, you can see that it has logged to indicate that its viewport changed height. (This height-change is from the toolbar appearing and/or disappearing while that tab is focused.) EXPECTED RESULTS: The toolbar-hiding-behavior should not cause the viewport of the testcase to change height. Conceptually, the toolbar should only be present for the new-tab page; the testcase shouldn't incur layout-jank as a result of that toolbar being hidden from the tab-switch operation. I ran into this "in the wild" at Google Photos -- I was viewing a large photo which is scaled to fit my viewport, and I noticed that there was a visible "jump" in the photo rendering whenever I switched from a new-tab to the Google Photos tab. (It would briefly render at the smaller toolbar-smooshed size, and then render at the full viewport size.)