There are three images below, but in summary with only two tabs open when the media player is not visible the memory use went up to 7GB (and would have kept on going) after about 10 minutes, and this is with no interaction with the browser. Selecting the media tab the memory instantly drops (but it is still a very high number).
Memory at start.

Select the other tab and leave for 10 minutes.

Select the media tab and memory drops, but still very high for two tabs.
