The Proxy SwitchyOmega extension (Chrome), or something like it, would be a good way to do this, too. https://duckduckgo.com/?q=proxy+switchyomega&ia=web.
Proxy SwitchyOmega installs on Orion, and it can be configured, but the extension icon (which lets one switch) does not do the right things in at least three ways: it doesn't offer the full list of configured proxies, it goes blank when attempting to switch proxies, and it doesn't allow [Direct] when there is a system http proxy configured.