This posting is older than 6 months and can contain outdated information.
There was a post a little over 2 years ago on Netflix actions:
Space – Toggle Play/Pause
Enter – Toggle Play/Pause
PgUp – Play
PgDn – Pause
F – Full-screen
Esc – Exit full-screen
Shift+Left arrow – Rewind
Shift+Right arrow – Fast Forward
Up arrow - Volume Up
Down arrow - Volume Down
M – Mute toggle
In full-screen mode:
Ctrl+space
I tried this on Mac OS 10.10 (Yosemite) but the F- (full screen) and Ctrl+space (Mute in full screen) don't seem to work. Also, I'm not sure if the 'com.apple.webkit.pluginprocess' identifier is still valid for the silverlight plugin. (at least I did not see this process in Activity Monitor.)