1326963 - Tabs don't slide (animate) correctly if I close "child" tab

Status: NEW

(Firefox :: Tabbed Browser, defect)

Description

[arni2033]

>>>   My Info:   Win7_64, Nightly 49, 32bit, ID 20160526082509
STR_1:
1. Open many tabs to cause overflow in tabs toolbar
2. In penultimate tab open the following url:   data:text/html,<a href="http://ya.ru">Link</a>
3. Middle-click the link. Shift+Middle-click the link
4. Scroll tab strip to the very end
5. Hover mouse over selected tab and middle-click it

AR:  Tab with ya.ru closed. The last tab didn't move at all. Other tabs moved to the right by 1 tab
ER:  The last tab should move to the left, just like it always works with normal not "child" tabs.
     Other tabs shouldn't move at all.

Reference of good behavior:  Try the same STR w/o overflow in tabs toolbar.