Firefor urlbar dropdown list not showing anymore

On my Linux machine, after using firefox for a while, I often suddenly notice that the urlbar dropdown list is not showing anymore when I type in it. No auto completion, no dropdown list, no anything.

I used to restart the firefox and it got fixed. But this is very annoying.

Now I found it might be because of the ibus input method. After I switch on and off the Chinese input method, the urlbar dropdown list and auto completion is back.