Rated 4 out of 5 stars

yazan: kinor tarih: Ara. 18, 2015 ·

Has worked rather well so far, however over the last few days YouTube seem to have changed something, as is their wont, so now the alert appears briefly every time again. Would you please look into it. Edited: the alert appears briefly on all sites.

This review is for a previous version of the add-on (1.0-signed). 

yazan: Vasiliy Temnikov (Geliştirici) tarih: Oca. 7, 2016 ·

Use version 2.0
https://addons.mozilla.org/ru/firefox/addon/hide-fulscreen-alert/versions/