Firefox has a great little built-in tool that most users don’t know about. It’s called Reader View and it’s right there on the URL bar:
It’s a toggle. Click it once to activate. Click it again to deactivate.
What it does is strip away clutter like buttons, ads and background images, then changes the page’s text size, contrast and layout for better readability. Check it out.
Before Reader View:
After Reader View:
That menu on the left can be used as follows:
You’ll find more details here.