User Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0 Build ID: 20171206182557 Steps to reproduce: I simply connected to some websites, for instance https://www.libreoffice.org/ or http://www.jeuxvideo.com/ Please note that you have to clear the cache before (just do Ctrl+F5). Actual results: On https://www.libreoffice.org/, I could see this bad layout for a few milliseconds : http://ratm6.free.fr/captures_d'ecran/libreoffice_org_ff.jpg Expected results: The layout should be good immediately.

This issue also happens with Firefox beta 58.0b11 and nightly 59.0a1.

Some other websites affected : https://wiki.mozilla.org/RapidRelease/Calendar and https://github.com/gorhill/uBlock/releases