Make a Long Firefox Article Easier to Read Without Changing the Whole Display
If a long article is surrounded by distracting controls or uncomfortable text, Firefox Reader View may help. It changes how supported article content is presented, letting you adjust the reading layout without altering the size of every application on the computer.
Try it on a suitable page
Open the article and look for the Reader View icon in the address bar. It appears when Firefox recognises suitable content. Activate it and use the text controls to adjust size, line spacing and content width. Change one setting at a time until a paragraph is comfortable to follow.
Inspect the available theme choices for a background and contrast that suit your environment. A very narrow column or unusually large text may require frequent scrolling; test a complete section instead of judging only the heading.
Check what the simplified view contains
Compare the title, an important paragraph and any essential table or illustration with the original page. Reader View is a reading aid, so return to the website’s normal view when you need interactive controls or content that was not included. Missing material in the simplified view does not mean it was deleted from the website.
Read aloud may be available when the computer has appropriate text-to-speech support for the article’s language. If it is absent, check that language support rather than treating the missing control as a speaker fault. Keep the volume appropriate for nearby people when reading private material.
Use the Reader View icon again or the exit control to return to the normal page. If every application is too small, a system accessibility or display-scale setting may be the more useful adjustment. This page-level method is intended for a different scope.
Source: Mozilla Support.