With Firefox 38.0.5 release, Mozilla has introduced Reader View feature, which when activated, presents the page to the user in clutter-free format by removing unnecessary elements such as ads, menu items and other items that comes in your way when reading. First of all, when a page supports Reader Mode, its icon (open book) will appear in the Firefox address bar, which you need to click to enter. Similarly, you need to click on the same icon again after reading to exit or close the Reader View. Till now Mozilla has not created a keyboard shortcut for the Reader view, now there is one.
Use the keyboard shortcut, don’t need to click on Reader view icon
Firefox Reader View keyboard shortcut
You can open and close Reader view in Firefox with the below shortcut on Windows and Mac platforms.
You can use this shortcut to toggle the reader view. Do note, you can’t force the reader view to appear for an article, that doesn’t support by using the shortcut, it’s icon must appear for you to use this and will work from Firefox 50 onwards, which by using the Reader Mode offers an option on the print preview toolbar to simplify page printing.