Firefox
Click the Menu button  > Help  > About Firefox
 

or for older versions:
Click Help on the menu bar > About Firefox
 
Chrome
Click on the Menu button > Help > About Google Chrome
 


or for older versions:
Click on the wrench icon > About Google Chrome
 
 
Edge
Click the Menu button > Help and Feedback > About Microsoft Edge
 
 
 
Safari
Click the Safari menu > About Safari
 


Opera
Click on the Opera logo in the top left > Go to Help > About Opera