Fixes a subpart of #230 : if I put %FIREFOX_HOME%\firefox.exe in my PATH (instead of %FIREFOX_HOME%), the enforcer rule is not satisfied and the build fail - without any output, but this is another issue.
Merge pull request #231 from Riduidel/fix-for-230-part-2

Fixes a subpart of #230 : if I put %FIREFOX_HOME%\firefox.exe in my PATH...