When you install this addon, you may click the ellipses, then click the addons tab, then click on this "Mobile Fullscreen" tab.

Finally, you may enter the fullscreen, and by means of this addon add such functionality to Firefox on Android, whether on phone or on tablet (ie. Boox Tab Mini C), where such functionality was not available before.

And this addon does so without hassle, and does exactly as it does. I may use this on the comipo app website with my Boox Tab Mini C, which has suffered such lack of functionality, and I may enjoy the light novel or manga, without such hindrances that which decrease the screen area, such as the URL display; and I may see the material to it's fullest resolution, that is, it's largest size that can be displayed, and by this I am benefitted.