For a long time I used to just disable CSS in Firefox (View, Page Style, No Style), which gives a readable page most of the time. I knew about Reader View, but because it only allowed low contrast gray text, and because I already had a workable solution, I dismissed it at worthless.

I recently noticed that I was using No Style so frequently that it would be worth checking for a better solution. I found it's possible to fix the low contrast text in Reader View with custom userContent.css:

    @namespace url(http://www.w3.org/1999/xhtml);
    @-moz-document url-prefix("about:reader") {
    body {
      background-color: #FFFFFF !important;
      color: #000000 !important;
      }
    }

No Style is still occasionally useful to get something readable where Reader View fails, but now I use Reader View most of the time instead.