The FireFox' disk cache foler is set to D:\Cache (I set it so from about:config).
I cleared the disk cache, watched a YouTube video (almost 2 minute long), then looked into D:\Cache. But the video I had watched was not there! (I found two .SWF files. But their sizes were smaller than 250K. And, stand-alone SWF players couldn't play them. Therefore, they can't be YouTube videos.)
So, where does Firefox cache videos?
Solved! Go to Solution.
Firefox doesn't cache videos on disk. The Flash player that plays the videos is in the cache, but the videos are streamed and not saved. They may be kept in the memory cache during the play.
You can check the cache on the about:cache page.
Firefox 9.01 saves videos in the usual cache folder, as I found.
In case you don't know how to locate the videos, follow this procedure. In Firefox' Location Bar, type "about:cache" (without quotes) . Look under Disk cache device for Cache Directory. Open that directory in Windows Explorer and search for "*.*" (without quote). Sort the results by file size. The biggest file(s) should be video file(s), although they have no file extensions. Windows Media Player can recognize video files without explicit file extensions and play them.
Remember to clear Firefox' cashe immediately before you open the URL that leads to the video.