An artifact is displayed for a millisecond after a snoozed tab is re-scheduled

[SoftVision-EmilPasca]

[Affected versions]:

• Release 58.0 and up
• Snooze Tabs 1.0.21

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have a Firefox profile with the latest Snooze Tabs add-on version (https://669-15314951-gh.circle-artifacts.com/0/tmp/circle-artifacts.kZdit8p/addon.xpi) loaded as a temporary add-on.
• Have at least one snoozed tab in the "Manage Snoozetabs" panel.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisite and navigate to a website.
2. Click the "Snooze Tabs" button from the toolbar.
3. Go into the "Manage Snooze Tabs" panel and click on the "date/time" button for one of the tabs.
4. Choose any date and time and click the "Snooze!" button.
5. Observe the edited tab in the "Manage Snooze Tabs" panel.

[Expected result]:

• The snoozed tab is correctly displayed in "Manage Snooze Tabs" panel.

[Actual result]:

• The snoozed tab displays an artifact for a millisecond, just before it is re-arranged in the panel.

[Notes]:

• Attached a screen-recording of the issue:

• A similar issue can be observed when having multiple items in the "Manage Snooze tabs" and scrolling up/down.

[lmorchard]

For re-snoozing, I think this close to as intended - we wanted to animate the old deleted item fading out and the new item appearing. The change is more dramatic if the change puts the item in a different spot in the list sorted by time

I don't see an issue in the scrolling clip, though. It looks like the sliding animation is working as expected when the mouse pointer moves

[SoftVision-CarmenFat]

The black artifact also appears sometimes when scrolling - you can see it better at the 17th second in the following video: https://goo.gl/qYLuNn.

[lmorchard]

@johngruen Were you still looking into this one too?