Some sites do show estimated reading time for an article on their site, Medium does that. Inspired from Medium, Mozilla wants to show reading time in Reader Mode for Firefox browser, a patch has been landed for that in the latest Firefox 53 Nightly, which does display the time in minutes on top it takes the user to read the story while in Reader View.

READ: Firefox 49: Enable Night Mode for Reader View

Firefox adds ‘Narrate’ feature to Reader View

And the Firefox Reader View keyboard Shortcut is