According to Wikipedia,

In order for all browsers in an organization to be supplied the same proxy policy, without configuring each browser manually, both the below technologies are required:

  • Proxy auto-config (PAC) standard: create and publish one central proxy configuration file. Details are discussed in a separate article.
  • Web Proxy Autodiscovery Protocol (WPAD) standard: ensure that an organization's browsers will find this file without manual configuration. This is the topic of this article.

It is possible to have all browsers use the same .pac file without configuring each one manually (i.e. not specifying the location of the .pac file in each one, but letting each one detect it automatically)

But I haven't been able to find one site where it says in plain English how to do this.

Is the article on Wikipedia wrong or have I misinterpreted what it says?

If neither, can anyone help me with the above?

  • I'm not aware of any auto-discovery or auto-populate for proxy pac file. In a domain environment you would do this with a Group Policy..
    – CharlesH
    Dec 22 '14 at 14:34
  • could you clarify your question: are you trying to just share the same PAC file among different browsers on your computer, or to provide a default PAC file to all users on a LAN? what operating system(s) are you targeting? do you want to profile default proxy settings or to lock proxy settings on the computer(s)?
    – Ale
    Mar 19 '15 at 23:05
  • "trying to just share the same PAC file among different browsers on your computer" - yes. I'm on Windows. Mar 20 '15 at 9:18

Firefox is the outlier in this case:

Most applications respect the WinINET proxy setting, but a few do not.

  • Firefox respects the WinINET setting only when configured to “Use System Proxy Settings” in its Network configuration.

In order to automate this, use a script which:

  • Copies the PAC URL to the clipboard
  • Applies it to the registry
  • Opens the Firefox preferences for the each subdirectory in the profile folder
  • Applies it to the prefs.js file in each profile

For example:

# To configure the proxy server settings on a client computer, create the following .reg file to populate the registry with the proxy server information:


[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings]

And in Firefox:

pref("network.proxy.type", 5)

If you need to set a PAC URL, use the following:

pref("network.proxy.type", 2)
pref("network.proxy.autoconfig_url", "http://ProxyServername:80")


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