[Bug 2047262]

[Nanoblade9]

I'm not sure if I'm having the same issue but Firefox doesn't prevent
screensaver from activating on my system. I can reproduce this on both
ESR and the latest Nightly.

```
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::WakeLockTopic() created video-playing
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::SwitchToNextWakeLockType() WakeLockType Initial
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0]   switched to WakeLockType FreeDesktopScreensaver
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5cfbcafa00] WakeLockListener topic video-playing state locked-foreground request lock 1
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::InhibitScreensaver() state uninhibited
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::ProcessNextRequest(): recent state uninhibited
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::ProcessNextRequest(): next state inhibited
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::SendInhibit() WakeLockType FreeDesktopScreensaver
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] InhibitFreeDesktopScreensaver()
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::DBusInhibitScreensaver()
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::DBusInhibitScreensaver() proxy created
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::DBusInhibitFailed() Inhibit call failed : GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.ScreenSaver was not provided by any .service files
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::DBusInhibitFailed(1)
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::SwitchToNextWakeLockType() WakeLockType FreeDesktopScreensaver
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0]   switched to WakeLockType FreeDesktopPower
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::SendInhibit() WakeLockType FreeDesktopPower
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] InhibitFreeDesktopPower()
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::DBusInhibitScreensaver()
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::DBusInhibitScreensaver() proxy created
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::DBusInhibitSucceeded(), mInhibitRequestID 16
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::ProcessNextRequest(): recent state inhibited
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::ProcessNextRequest(): empty queue
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5cfbcafa00] WakeLockListener topic video-playing state unlocked request lock 0
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::UnInhibitScreensaver() state inhibited
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::ProcessNextRequest(): recent state inhibited
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::ProcessNextRequest(): next state uninhibited
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::SendUninhibit() WakeLockType FreeDesktopPower
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] UninhibitFreeDesktopPower()
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::DBusUninhibitScreensaver() request id 16
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::DBusUninhibitScreensaver() proxy created
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::DBusUninhibitFailed() UnInhibit call failed : GDBus.Error:org.xfce.PowerManager.Error.CookieNotFound: Неверные данные 
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::DBusUninhibitFailed()
[Parent 13156: Main Thread]: D/LinuxWakeLock [7f5ce86424c0] WakeLockTopic::Shutdown() state inhibited
```

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https://bugs.launchpad.net/bugs/2047262

Title:
  Firefox stopped inhibiting screensaver on video playback

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