In order to install the theme & font size
changer do search for this in your browser and go to the add-ons page and once you have done that you will be asked to add this to Firefox. A pop up box will appear asking about software installation, if you install now. Once you have installed this add-on you
will now see an additional icon in your menu bar. So that’s how to install ithe theme, font and size changer add-on for Firefox.