Linux Mint 13 (both 32 and 64-bit versions), Control Center -> Preferred Applications -> Internet settings are not working properly.
1. when set to Custom (Web Browser, Mail Reader), all fields stay greyed-out so there is no way to enter "custom" command
2. setting to predefined application (e.g. Web Browser to Firefox) does not change the binding, even for the HELP button on the VERY SAME window. Apparently most (all?) components use /usr/bin/sensible-browser script which, on my system, invokes Chromium, unless I change it with "alternatives" mechanism, which requires root priviledges and totally ignores "Preferred Applications" settings.