No context menus when using Samsung DeX mode/external mouse
When using Firefox on a Galaxy S device under DeX mode (same behavior on my S9 and Tab S5e), Firefox does not provide any context menus via either a long-left mouse-button press or a right mouse-button press. Other browsers (Chrome, the default Samsung browser, etc) do give context menus via a right-click, but FF does not. I can't open links in new tabs, request a link be opened with an external app, etc.
I can get the conext menu if have Dex use my phone as the pointing device, but that's not (generally) how I have things set up. It does not work if I use the touchpad on my NexDoc laptop.
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