[omaranto]

I don't know what cmd means (I'm kidding, I have seen Apple computers even if I've never used one), but you can find out what the keyboard shortcut is on your own copy of Firefox by hovering the mouse over the Reader mode icon. On my Firefox it says "Ctrl + Alt + R".

[michaelmrose]

They added reader mode to firefox for android in 2012 it took them 3 years to add this to desktop firefox and almost a year to actually add a hotkey that you can't configure.

Firefox 38 for reader 50 for a hotkey.