Have you tried pressing F11?

I I want to see apps all the time. I didn't mean the vertical full screen, full screen on the both side. now I see is the web site in the center, and both right and left is open.

You can use one of these extensions to set a default font size and page zoom on web pages:

• Default FullZoom Level: https://addons.mozilla.org/firefox/addon/default-fullzoom-level/
• NoSquint: https://addons.mozilla.org/firefox/addon/nosquint/

I'm still not sure what you are saying. Are you trying to fit the content of the web site screen to the width of the browser window?

You can try holding down the Ctrl key and using the scroll mouse button for that.

If I understand correctly, just hover over the side edge of the page and when you get a double-headed arrow just drag it to the side of your screen.