If you read a lots of articles on the Internet, you are usually easily distracted. There are flashing/moving adverts, the text might not be the best size or even the background is chosen poorly.
Have a look at Readability. Their slogan is "Transform any article into a clean, comfortable reading view - instantly". It leaves only the main article behind, some metainformation and obviously the pictures for that article. You can adjust the contrast, the font the way you like it to improve readability.
Their new model is now subscription based. The majority of that goes to the actual website, a minor part to Readability. I suppose this is for loss of revenue through banners and adverts.
You can try it for free via their Add-On on Readability for Firefox. A Bookmarklet is available here. It seems that the Firefox Extension from Mozilla Add-Ons is outdated.