How the _isexecutable function is set up now it would require a full path name in order to be able to tell if a specific browser is on the system. The area under platform support for windows checks for multiple browsers using this function but only passes it browser names and so it always returns false and does not add any browsers to _tryorder. I found a way to fix this using os.walk so that the simple strings of the browser names like "firefox.exe" is able to actually able to be found on the system. This method is rather slow though and the module wants to check for 8 browsers when imported.