Sometime ago I wrote about VideoCacheview to view, copy, extract videos, audios, images stored in browser cache. This application works in Windows computer only. If you are using Linux or Mac then you can try CacheViewer addon for Firefox. You can easily view and save video on your computer by viewing all the stored cache files (without using any tool you can’t save videos stored in browser’s cache. You can view those files by typing about:cache in your browser’s address bar).
Download and install the extension on your PC (link given at the end). After restarting the browser, go to Tools –> Cacheviewer (or you can use keyboard shortcut Ctrl+Shift+C).
It will open all the Firefox cache files stored inside your computer. It means if you run any video, audio or view images in your Firefox browser then you can view all those files stored inside your browser’s cache. Since there are large number of cache files, you can filter the video or audio files using the inbuilt search box. Just enter “YouTube video” without quotes inside the box and press enter. You’ll get all the video played by you in YouTube.
Right click on the file and select “Save As” option to save the file on your PC. You can save the file in any location of your PC. If you watch videos on Firefox and want to save all the video files later then it is better to increase the Cache space assigned to Firefox (by default it is 50 MB), you can increase it to 100 MB so that more and more videos can be saved inside cache. In Firefox go to Tools –> Options. In the options panel, click on the “Advanced” tab and then click on “Network” tab. Here in the “Offline Storage” area, increase the value of cache space.
Note: Increasing Offline Storage may affect your browser’s speed.