Automatic download of OpenH264 plugin

[Viktor Jägersküpper]

Dear Mozilla Maintainers,

> Setting
> 
> media.gmp-gmpopenh264.autoupdate = false
> 
> prevented the automatic download

this is wrong. It seems that Firefox since version 50 automatically
checks for updates of extensions and plugins at the same time, so
checking for updates leads to the automatic download of the OpenH264
plugin in the default configuration (in Debian). From the release notes
of Firefox 50:

"The link to check for plugin security updates has been removed from the
addon manager as Firefox automatically checks for plugin updates"

To prevent the automatic download of the OpenH264 plugin one has to set

media.gmp-provider.enabled = false

or even create media.gmp-manager.url.override = data:text/plain,

Maybe one could consider this a bug in Firefox (upstream), because
"update" could be understood as updating something which is already
there, so if someone sets media.gmp-gmpopenh264.autoupdate to false, and
then checks for updates of extensions/plugins, one would not expect the
download of the plugin. If you want me to report this as a new bug in
Mozilla's Bugzilla, please tell me. I don't think that any of the open
bugs in

https://bugzilla.mozilla.org/show_bug.cgi?id=openh264

refers to what I observe.

Regards,
Viktor