@bec did you change the settings in mplayerplug-in.conf?
I don't know if the settings for setting speed on nrk-nett tv, and if it works outside Norway. Maybe you have to reboot to get it inside microb?

I used mplayerplug-in_3.50-1_armel.deb and not the 3.55, but don't think that should be a problem.

You could try changing settings in mplayerplug-in.conf
http://mplayerplug-in.sourceforge.net/config.php

noembed=0 would start mplayer inside the web. I used noembed=1 since it worked better for me.
My mplayerplug-in.conf now only has one line: noembed=1

I upgraded the plugin to the 3.55 and it still worked.

With noembed=1 you can use the keystrokes on the keyboard sending mplayer-commands.