Mac

1. Select the Firefox menu, then "About Firefox."
   
   
   
   
2. In the display window, the version will appear below the word Firefox
   
   

Windows

Newer versions of Firefox

1. Click the Menu button in the top right corner
2. Select the Help option at the bottom of the menu that appears - this is denoted by a question mark
   
   
   
   
3. Select "About Firefox"
   
   
4. A dialogue box will appear and the version number will be located underneath the word Firefox
   
   

Older versions of FireFox

1. Select Firefox in the top left-hand corner, then hover over the "Help" option to open the drop-down list and select "About FireFox."
   
   
   
   
2. In the Window that pops up, the version will appear below the word Firefox