Do you remember, a couple of weeks ago, I explained on how Gmail was broken on Firefox for Android. I was finishing my post with:

Basically it seems that in Blink world the border-width is taking over the border-image-width. This should be verified. Definitely a difference of implementation. I need to check with David Baron.

I was wrong, it's a lot simpler and indeed David helped me find the culprit.

http://www.otsukare.info/2016/03/17/fixing-broken-gmail