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Sadly mozilla provides no documentation for those settings, but I can assure you that this setting does not care if the tab is in the foreground or background,
by bigbugbag 9y ago
Sadly mozilla provides no documentation for those settings, but I can assure you that this setting does not care if the tab is in the foreground or background, autoplay is simply disabled which it seems to me was what was asked here IIANM.