The following code:

  // If the background (non-current) BVC is playing TTS audio, call
  // -startVoiceSearch on it to stop the TTS.
  BrowserViewController* backgroundBVC =
      self.mainBVC == self.currentBVC ? self.otrBVC : self.mainBVC;
  if (backgroundBVC.playingTTS)
    [backgroundBVC startVoiceSearchWithOriginView:originView];
  else
    [self.currentBVC startVoiceSearchWithOriginView:originView];

should be changed to:

  BrowserViewController* backgroundBVC =
      self.mainBVC == self.currentBVC ? self.otrBVC : self.mainBVC;
  if (backgroundBVC.playingTTS)
    [backgroundBVC stopVoiceSearch];
  [self.currentBVC startVoiceSearchWithOriginView:originView];