Having learned a bit more about what add-ons/extensions can do in Firefox, I want to minimize my risk and use some safer mechanism to download videos (FLV in particular) for later viewing.
Considering the question What are the security implications of people downloading plugins, wrongly thinking that they are safe?, is there any way to trust an (open source?) browser add-on? I can examine the code myself if it's not 100,000 lines of illegible gunk.
The most popular video-downloader add-ons are closed source AFAIK.