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>>> My Info: Win7_64, Nightly 47, 32bit, ID 20160229030448 STR: 1. Open new window, open 5 tabs in that window. 2. Open attached "testcase 1" in the last tab in that window (dont' click on the page!) 3. Allow opening pop-up windows 4. Click on the page, then within 2 seconds start dragging selected tab: Hover mouse over selected tab, hold left mouse button, move mouse pointer a bit to the left 5. Wait 3 seconds (do not release left mouse button) 6. Slowly move mouse pointer to the right side of the first tab 7. Slowly move mouse pointer to the left side of the last tab AR: After Step 5 you end up dragging background tab In Steps 6 and 7 that tab lags (twitches) a lot. I.e. is not smooth at all. ER: X, or Y, or Z (see Note 2) X) In steps 6 and 7 the tab should not lag/twitch. Should be smooth like in Firefox 28 Y) Dragging background tabs should be fixed (for add-ons) and in default Firefox install background tab should be selected if I drag it Z) Any other clever option defined by developer, which won't worsen my UX (including add-ons) much Note: 1) This is regression between Firefox 32 and Firefox 38 2) Somebody may think that the right solution is just to prohibit dragging background tabs and select tab if it is in "drag-n-drop" mode. Well, there're some extensions that allow dragging background tabs (e.g. Multiple Tabs Handler), and they were broken by this regression. It'd be good if they could work normally, without hacks overriding default Firefox behavior.
Use case: Sometimes I click a link in Mozregression GUI, and that application lags for a while. So I'm able to switch to Firefox window, and do some actions, e.g. to start dragging a tab. And then eventually a new tab opens. So I run into this bug. Make sure you read Note 2.
Oh, sorry. Comment 3 happens with many applications that open link in default browser Mozregression GUI is just one of them. This happens with every such application.
The twitching of background tabs was added in 2 steps. Before (1) - everything was OK Between (1) and (2) - background tab sometimes teleports to a new position during Steps 6-7 After (2) - background tab twitches a log during Steps 6-7 1) Bug 927349 (between 2015-01-05 and 2015-01-06). Regression range: > https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=636498d041b5&tochange=2a193b7f395c 2) Bug 980770. Regression range: > https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=ef53c6c25fb19341f42858d57434b4b8685f2555&tochange=eed5d2d610e28f05c4e561ce16360cddc1661955
Summary: It's possible to (A) drag background tab (B) that tab lags a lot → A window opening while dragging a tab can result in janky dragging of a background tab
Platform triage meeting discussion: This seems to be an old regression which is polishy in nature. Wontfix for Fx47.
This is regression with CSS "transform" property; I also have several other examples of this. Its nature is that elements twitch enormously when you set new transform value, just like in comment 0. Such graphic regressions are never called "polishy" on my memory, and never presented on more than 2 releases (if detected soon enough). However, the fact that this bug was reported by _me_ automatically makes it "polishy" in developers' opinion.
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