Firefox: Save a webpage as plain text with one key combination (no dialog box!)

my question is what is the most straightforward way one can save a web-page (in Firefox) as plain text file using a single key combination (like Ctrl+S or something similar), without hitting any "Save as" dialog box.
(I looked for mimetypes.rdf on my Windows machine, but could not found it. I also read that changing this for "inteal" application types is not allowed.)
Could you please suggest what options does one have (sure, addons are also welcomed) in this case? I am out of ideas.. :)
Thanks & cheers, M.

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