Few weeks ago I've discovered a really nice Firefox extension, called TV Manager, that allows me to find quickly the answer to one of my most frequent questions: What's on TV tonight? TV Manager gathers television listings from different countries and channels and displays them in the browser sidebar in a convenient way.
At the moment, TV Manager can be installed only registering to the Mozilla Addons site: this is due to the fact that Mozilla editors didn't review it and make it public. I encourage you to write a review about TV Manageron the Mozilla site: more reviews an extension gets, more likely it becomes public.
TV Manager has been also certified 100% clean by Softpedia. It is definitely worth to give it a try!