The "three dots" menu is the Chrome Menu button, hit ALT and you have focus on it. Hit either Enter or Down Arrow and it opens.
If you ever hear the description of either the "three dots" or "hamburger stack" menu or menu key, you can be virtually certain it's the browser's main menu key and that ALT will throw focus to it. In the case of Firefox, though, ALT still brings up the old menu structure, which gives you access via a different route to all of the things that the Firefox main menu key (hamburger stack type, in this case) does.
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
A great deal of intelligence can be invested in ignorance when the need for illusion is deep.
~ Saul Bellow, To Jerusalem and Back