I recently had an issue with the latest version of Firefox (v3.6.15). Normally, when we install Firefox on our network, we have to change the proxy settings from the default “No Proxy” to “Auto-detect proxy settings for this network”. This doesn’t normally cause much of an issue as we only use Firefox on a few select machines and can be changed by the individual user. However, it seems the default install behaviour has slightly changed to add a new option that seems to muddy the water. There is now a “Use system proxy settings” option (similar to Google’s Chrome) that seems to be selected by default for new users. Although this may seem to make sense, on our network this causes terribly slow page load times, e.g. 10 minutes to load google.co.uk. Luckily I found a way to set the “Auto-detect” option for all users.
WARNING: This seems to have changed again since Firefox 4 was released. If anyone knows how to change it please add a comment.