ivayo, thank you for all your efforts.
The reason I am not using Totem's Mozilla plugin despite the fact that it
works in Epiphany, Midori and in Mozilla based browsers is because the full
screen controls are dreadful. The URL of the video covers most of the bottom
region in full screen mode so I can not seek on my netbook (see this
screenshot). ROSA's controls are much better in full screen mode and it works
in all the browsers Linterna Mágica supports (unlike Gecko Media Player
which only works with Mozilla based browsers).