This extension works fine with a web page (which is a typical feature of others tools like this), BUT the reading from a pdf or epub file is the coolest feature because it's the typical case use for practicing speed reading.

Good work!

best i found for firefox

This is exactly what I wanted, thank you!

Is there a scope of improvement? I believe so. With EPUB this add on works well. WIth PDF, this extension functions well, but the page is squished and mostly unreadable. Hopefully, later versions add page width, for readability.