doesn't work at all! Shows white page. Even though source is valid JSON and header set correctly. Linux 3.16.0-4-amd64 #1 SMP Debian 3.16.51-2 (2017-12-03) x86_64 GNU/Linux Firefox ESR 52.5.2 (64-bit)
Please set webextensions.storage.sync.enabled to true in about:config as there is a bug in Firefox 52 https://bugzilla.mozilla.org/show_bug.cgi?id=1331179
