I seem to recall that you're using Firefox, Henry!
Assuming that you are (and you want to know the version number), have you got 'File, Edit, View, etc' across the top of your screen? If so, simply go to Help > About Firefox.
If you've not got 'File, Edit, View, etc' across the top of your screen, right-click near to the top of your screen and click on 'Menu Bar'. (Then proceed as above).
Those instructions might well work with other browsers as well (although, of course, the word 'About' will be followed by something other than 'Firefox').