Use a quick mode switcher in the context menu of the button bar icon

[machawk1]

Based on the Chrome extension, "User-Agent Switcher", which provide the option to switch from a "black-list", "white-list", or "custom" mode

For comparison, the current version of Mink in the issue-316 branch (adapting for MV3) is the base interface.

Which Chrome API allow this to be customized? Document this here and explore which sort of quick options might be the most useful.