The process for reading HTML and then spitting out a new stylesheet in order to make reading the boards easier is straightforward.

Both formats have language methods for reading HTML and then running that content through a stylesheet with the purpose of displaying a new layout of the boards in the browser.

The extension would likely have to be written in Javascript and then that script could spit out a CSS stylesheet which would act upon the HTML and display an 'updated' board.

If you have some spare time and are still interested, I could workout some ideas for layout and the programming structure and then post them in a Google Document of some sort for you, or anyone else, to read over.