Hi there,
if Netflix still uses Flash, then I'd suggest to use Google Chrome instead. The last forum threads here regarding netflix are quite dated, and most people eventually seem to have been successful with Chrome.
If you still want to get it to work with Firefox (and if Netflix still uses Flash as mentioned) then you need a current flash plugin (which is called pepperflash and comes bundled with Google Chrome) and to install freshplayer, which is a wrapper so that firefox can use that plugin. At least that was the situation when I last looked at it, maybe some other Netflix users can chime in and add their 2 cents
In any case, we have both a MAQeia for Chrome
viewtopic.php?f=36&t=2053 and one for Flashplayer:
viewtopic.php?f=36&t=880