Would be nice if netflix somehow can save that setting at your account so that it's automagically used when playing videos...
Actually, this IS how it was working in the plugin. I used to just play a video in my browser, switch on subtitles by (As you said) hovering over the relevant control and enabling, then, when I watched videos in the MP Plugin, I would get subtitles. So, something has changed somewhere, because I see subtitles when I watch in a browser, but not when I watch in the plugin?