Firefox doesn't enable Reader View on every page. When Reader View is available, you should see a "book" icon in the address bar. Please see the attached screenshot.

When I tried it with a text file, Firefox didn't read the text. This may be due to the particular file I tried or some issue with text files in general. Since the feature is so new, I'm not sure exactly what to expect there.

Edit: Here's the general help article on Reader View for desktop versions of Firefox: Firefox Reader View for clutter-free web pages.

I noticed this extension to let you "force" Reader View for a page without the icon, but didn't try it myself: https://addons.mozilla.org/firefox/addon/activate-reader-view/

Thanks. Did a search of the web and found an article at ghacks.net which outlined the steps to take to enable reader mode. Reader Mode was already enabled fortunately. Went out to a Wikipedia article and saw the little book icon, clicked on it, and was pleasantly surprised to hear intelligible speech. Had the same experience as you -- the file didn't work at all. I'm sure that there is a app out there which does text to speech on files. Just got to find it. Again, thank you very much. John