My embedded WebExtensions has a browser action with a popup that resizes frequently for different reasons. On Windows 10 with Nightly 56.0a1 (2017-07-15) (64-bit) the popup sometimes goes invisible, because it gets resized to 0 by 0px and the browser unloads the content file (at least that's what I've been able to see with the browser toolbox). It seems this only gets triggered when the content document resizes from a certain point on. I can not reproduce this on Linux or with a pure WebExtension, though I assume the WebExtension I used does not hit the same timings for the resizes (and has no resizes upon user interaction). The version of my extension with which I encountered this issue is available from https://addons.mozilla.org/en-US/firefox/addon/justintv-stream-notificatio/versions/beta?page=1#version-3.4.0pre5