It appears as though Firefox requests web fonts (specifically Google's) in a different manner than other browsers. They fail to load when behind Squid as a result, and I'm trying to isolate why.
Using this page as a reference in various browsers, Firefox noticeably displays it differently.
In the Squid logs, you see hits like this:
TCP_DENIED/407 3292 GET http://themes.googleusercontent.com/font? - NONE/- text/html
If you load the same page with IE, you see hits like this:
TCP_DENIED/407 4389 GET http://themes.googleusercontent.com/static/fonts/federant/v1/C109bUmZeyhh-vIXq9lNfvesZW2xOQ-xsNqO47m55DA.woff - NONE/- text/html
So why the difference and how can we make it play nice with Firefox? This is running Squid 3.1.15, but also tested with a few other 3.1.x versions.