Comment 17 for bug 861443

MrCopilot;

We understand your frustration. Ignoring hosts for proxy is something that tends to be useful, but perhaps it was deemed not as frequently used as the other functions by upstream developers, which is why it's no longer exposed in the UI (which is something Ubuntu gets from upstream, so it applies to all distributions using Gnome3). As you undoubtedly have noticed, the option is still available via command-line, as such:

gsettings set org.gnome.system.proxy ignore-hosts ['localhost', '127.0.0.0/8', 'some.other.host']

However, the issue you're describing is something different than not being able to change proxy settings at all. As such, I'd like to invite you to file a new, separate bug report that covers *precisely and only* exposing ignore-hosts in UI. We can then send this report to the upstream developers at GNOME (alternatively, you can just file the bug there directly (see https://wiki.ubuntu.com/Bugs/Upstream/GNOME)). This way it will run the best chance of being taken care of by developers.