Ecstatic that I finally found this add-on.
Only caveat is that it can't do multiple paragraphs. Only the one you right click on.
Otherwise superb for reading those microscopic Amazon book descriptions. HAPPY

This extension is incredible because it still works after almost 5 years without any further development. Now I am able to increase the font size on text based pages without changing the page zoom. This extension is absolutely comparable to the Zoom Text Only extension in Chrome. The only drawback is that the font is enlarged in justification, but still well done.

No automatic zoom,useless

Claims to work on mobile Firefox, but doesn’t: “TypeError: browser.contextMenus is undefined”.