Note system scaling works out of box with Cinnamon desktop. Open a terminal window and install it with:
$ sudo apt-get install cinnamon-desktop-environment <enter>
To do system scaling in the Gnome Desktop Environment, install the gnome-tweak tool. To do so, open a terminal window and enter the command as below:
$ sudo apt-get install gnome-tweak-tool <enter>
To scale web pages in Firefox, you can use the Zoom option in the Firefox menu, or install Zoom Page WE Extension to scale the display upon the visiting of any web page.
In Chrome, the scaling takes effect by increasing the font size.