1247899 - [e10s] Closing SELECTED tab disappears immediately, and that (for 200ms) causes tabs resize if I move mouse pointer within tabs toolbar

Status: NEW

(Firefox :: Tabbed Browser, defect, P4)

Description

[arni2033]

>>>   My Info:   Win7_64, Nightly 46, 32bit, ID 20160210071115
STR:
0. Hide Titlebar, Menu bar, Bookmarks toolbar.
1. Open new firefox window.
2. Open enough tabs to cause overflow in tabs toolbar. Open ~5 more tabs. Scroll tabs list to the end
3. Select 3rd tab from the _end_ (or any tab except the last one)
4. Move mouse pointer between the tab start and tab title start (there's about 5-10px)
5. Middle-click where the pointer is placed, then (you've got 200ms of tab width transition)
   move pointer towards the next tab (within tabs toolbar).

AR: 3rd tab from the end closed, and tabs moved to the end of scrollable area (<tabs>)
ER: Tab from Step 3 should close, but tabs shouldn't move to the end of scrollable area,
    just like it works when Title bar is shown.

Notes:
1) It worked fine in Fx28-, but only because of CSS hack (see bug 1219215 comments 1, 2)
2) If there's not enough tabs to cause overflow in tabs toolbar, they just resize after Step 5.
3) This was NOT broken by bug 1219215; it's only a case that was missed in 1219215.

Comment 1

[:Gijs (he/him)]

Doesn't this happen without overflow as well?

Comment 2

[arni2033]

Yes. In Note (2) I tried to describe that.

Comment 3

[:Gijs (he/him)]

Hm. It's not clear to me off-hand why closing the selected tab is special here. Do you know?

Comment 4

[arni2033]

I have no idea. I barely have time to upload some bugs, so ofс I haven't read the changes in 1219215
Also, this is reproducible in about 5 of 10 times (i.e. harder than in bug 1219215). But with Titlebar shown it's 0/10. I guess Step 5 is wrong about 200ms - looks like a smaller interval.

Comment 6

[arni2033]

Oh, dang! Sorry for bug spam. I just read comment 2, tested everything again and realized that:
1) This bug happens as reported in comment 0 (w/o special case in comment 5), but only in e10s mode
2) Comment 5 does happen, but I'll report it separately/find a duplicate(s)