The previous patch writes the registry value correctly, but the Firefox
InstallerPrefs module deletes it during startup because it's in the
same key where the actual pref values go and the module unconditionally
deletes every value there. So making it only delete values that are
recognizably actual prefs should fix this.
Differential Revision: https://phabricator.services.mozilla.com/D53693
At least for now, this behavior is behind a hidden pref. The intent is to
experiment with the feature and determine that way whether enabling it
permanently is a good idea, and if so the pref gate will be removed in a
separate bug.
This patch depends on bug 1567247 and will fail to build without it.
Differential Revision: https://phabricator.services.mozilla.com/D41100
