Fixing Proxy Authentication Dramas on a Mac

I’ve had this weird proxy authentication issue that prevented me from connecting to the internet via Firefox on a Mac from behind a corporate firewall.

I switched a couple of authentication options for Firefox as shown below to solve the problem.

Step 1:
Open an instance of Firefox and type in “about:config” in the address bar. Click the “I’ll be careful, I promise” button.

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Step 2:
In the Search field enter “network.negotiate” and select the “network.negotiate-auth.allow-proxies” settings row. Double-click the row to change the Value to “false”.

If you’re using a Microsoft ISA proxy server, this setting effectively disables SPNEGO client-side and gets you through.  

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Step 3:
In the Search field enter “network.automatic” and select the “network.automatic-ntlm.allow-proxies” settings row. Double-click the row to change the Value to “false”.

If you haven’t attached your machine to a Windows domain, this setting prevents Firefox attempting to silently “single sign-on” to the ISA proxy using your non-domain credentials (and therefore failing the authentication challenge).

imageStep 4:
Go to Firefox -> Preferences -> Network -> Settings and click to select the “Auto-detect proxy settings for this network” radio button option.

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Step 5:
In the event that you need to use a Cisco VPN client to connect remotely, the latest version of the Cisco VPN client (v3.1 as of this writing) must be used. The above settings (Step 1 – 4) should work seamlessly, connecting you to internal and external web sites even when you’re on the VPN.

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