You could always use this plugin that I use to watch video in Firefox with your choice of mplayer or vlc player in the browser. You can use it for youtube and most any other site that has flash or similar. It will support all the videos that vlc and mplayer support respectively, best of all there is a configuration screen that lets you add/remove any site you want to a list, so you could use it just for comcast or for as many sites as you like!
Here's the link:
https://addons.mozilla.org/en-US/fir...without-flash/
It can literally replace flash with vlc or mplayer completely, though I don't recommend it for youtube I think it would be perfect for your situation considering you only need it for one site. Just make sure you have either the vlc browser plugin or the mplayer plugins which, even if you don't use this plugin, would be a good idea to install, and may solve your problem all together without the plugin.
The mplayer browser plugins are fantastic, they support windows media video streams and allow you to watch itunes trailers natively in Firefox just like your using safari. Plus, the cpu usage on youtube videos in Hd with vlc is like 5-8% with hw acceleration enabled (VA API)! The required packages are on slackbuilds I think. Hope this helped.
