investigate Firefox "debugger server" and Remote Debugging Protocol things

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--start-debugger-server [ws:][ <port> | <path> ] Start the debugger server on
                     a TCP port or Unix domain socket path. Defaults to TCP port
                     6000. Use WebSocket protocol if ws: prefix is specified.

[deepsweet]

https://developer.mozilla.org/en-US/docs/Tools/Remote_Debugging/Debugging_Firefox_Desktop

[deepsweet]

It's possible to change (per tab!) the following things using Remote Debugging Protocol (RDP):

• network throttling
• user agent
• DPPX
• touch events override

Unfortunately it seems to be impossible to control "viewport" like in Responsive Design Mode (RDM), it's done internally through manipulations of browser's "chrome" tool window:

this.toolWindow.setViewportSize(size);

It's not a part of the RDP.

So far I see 2 ways to get all the RDM functionality after switching to this._send('Marionette:SetContext', { value: 'chrome' }):

1. simulate bunch of shortcuts/keypresses to control RDM elements – this seems to be flaky and fragile
2. find out how to invoke ResponsiveUIManager() programmatically – it's bound to ctrl-shift-m somewhere in chrome context