Configuring FireFox to use Vim for View Source

Unexpectedly I had trouble Googling this, remember it is not in the standard Options Menu, no you have to go into "about:config"

in FireFox Address Bar type "about:config"

in the filter bar type "view_source" and configure following options as follows
view_source.editor.external user set boolean true
view_source.editor.path user set string c:\vim\vim.bat

rem contents of vim.bat
c:\vim\vim72\gvim.exe %1 %2 %3

NOTE it would be simpler to configure view_source.editor.path to point directly to c:\vim\vim72\gvim.exe but you'd have to remember to change next time Vim is upgraded