Making text larger in Firefox
Below are the step-by-step instructions on how to increase the font size in Firefox
Instructions
Follow these steps to increase or decrease the size of the text for the web page you are viewing:
Open the ' View ' menu with the mouse or by press ' Alt ' and ' V ' at the same time.
Select the ' Text Size ' option with the mouse or by pressing ' S ' twice.
Increase or decrease the text size with the mouse or by using the up and down arrow keys and pressing ' Enter '.
Alternatively you can press ' Ctrl ' and ' + ' to increase the text size, ' Ctrl ' and ' - ' to decrease the text size. ' Ctrl ' and ' 0 ' returns you to the default size.
Follow these steps to set a minimum text size for all pages you visit:
Open the ' Tools ' menu with the mouse or press ' Alt ' + ' T '.
Click on ' Options', or press ' O ', to open the Options dialog box.
Make sure that the ' General ' option is selected - if not either click on it or press ' Tab ' until it is highlighted (in blue) and then press the ' Enter ' key.
Click on ' Fonts & Colors ', or press ' F ', to open the ' Fonts and Colors ' dialog box (see Fig 1 below).
Click on ' Minimum font size ' box or press ' Alt '+' Z '. Use the up and down arrows to select a new font size and press ' Enter '.
Click on ' Always use my:' 'Fonts ' checkbox, or tab to this checkbox and press the ' Spacebar '.
Click ' OK ' button or press ' Enter '.
Click ' OK ' button or tab to ' OK ' button and press ' Enter '.

Fig 1
Note: If this does not work it could be because your computer settings cannot be changed due to local IT policies - contact your local IT support for further help.