Say I want to use a proxy auto-config file that is stored at C:\proxy.pac. To make Internet Explorer use this configuration I have to specify the pac-file in the LAN settings in the following way:

file://C:/proxy.pac

But Safari, that uses the same proxy settings, will ignore it in this case. To make Safari use the pac-file I have to reference it as

file:///C:/proxy.pac

(3 slashes at the beginning) which, according to Wikipedia is the correct format. But this way Internet Explorer will ignore it. Opera and Chrome, that also use the same proxy settings, are fine with both ways but is there another option that will work with Safari and Internet Explorer at the same time?