Today i updated my firefox to the latest version and one big feature is the reader view for desktop. We launched a webshop two weeks ago and now there is this tiny \"reader view
This Question shows how to Optimize website to show reader view in Firefox. So you have to ensure that your site is not optimized for the Reader View.
Don't use formatting options that are favoured for the Reader View and so on.
I guess this will suffice:
TagHere are some more details about the mechanism