If you need a simple,one click solution for this so that you can download your favorite video from internet then RealDownloader from realnetworks can enable the video download button for you.It is compatible with the latest version of Mozilla Firefox,Google Chrome & Internet Explorer as well.Either you can install the Real Player which is the recommended player for 3gp files from the link below
During the installation process you will see a screen as shown in the image below where you need to check the option "Enable browser download button" & continue with the installation.
Once you download the software,run it and click on accept as shown above
It will start installing the browser plugin for you,once its complete it will ask you to restart the browser as shown below
Once you restart the browser,Download This Video button will start appearing on top right of your favorite videos as shown below
Now you can download and save your favorite video to your computer so that you can watch it in spare time.