>>492
FireFox52以降でHTML5のH264動画を見る方法

How to make HTML5 H.264/AVC video work on Windows XP/XP x64 (using Firefox) ? The GAT at XIN.at
http://wp.xin.at/archives/4059


最後の下の方のは↓でOK
media.gmp-manager.url. Its value should look something like this: https://aus5.mozilla.org/update/3/GMP/51/%BUILD_ID%/%BUILD_TARGET%/%LOCALE%/%CHANNEL%/%OS_VERSION%/%DISTRIBUTION%/%DISTRIBUTION_VERSION%/update.xml