Description of problem:

I'm using firefox57. I try to use <Tab> key to change focus from "username" field to "password" field on a website for login, the gnome shell crash. 

What's more, when I use <Tab> key to change focus from "username" to "password", the input method switch table(which is on the right of the gnome top bar) disappeared. At this moment, if I was using the "US keybord" input method,nothing happens, but if I was using "Intelligent Pinyin"( for Chinese) or "Kana Kanji"(for Japanese), the gnome-shell crashed.

Sometimes when I click the "password" with mouse, it also crash.

you can visit this website for a try:
https://bugs.freedesktop.org/enter_bug.cgi?product=xorg