The tab structure has been broken.
I use only one tab group.
Of the whole structure, only the lower half was broken.
before.
aaa
.bbb
..ccc
...ddd
....eee
..fff
...ggg
....hhh
...iii
....jjj
..kkk
..lll
after.
aaa
.bbb
..ccc
...ddd
....eee
..fff
...ggg
....hhh
iii
jjj
kkk
lll
I think that it was broken when restarting firefox.
I am sorry, I do not understand any other occurred conditions at all.
I will only report that I encountered such a phenomenon.
Version 1.9.3
Edited by asami