Try getting an add-on from within Abrowser: (1) Open the menu in the top-right corner; (2) Click on "Add-ons"; (3) Select "Get Add-ons"; (4) Search for "video download" or "youtube" or something like that; (5) Choose one you think might work (installation is automatic).
See if it works for you. If you don't trust it you can remove it or disable it after you've used it. I can't recommend one for you because I avoid videos that absolutely require Flash because of the persistent cookies it installs all the time and because I want to keep my workstation 'clean'. I can still watch just about everything using an alternative.
In any case, installing downloaded packages like you described takes system administrator skills unless there is an install script.
