Check duplicate content / plagiarism.
How to use it:
1. Select any text on webpage (Press left mouse button at start of text, drag until the end of text, release the left button, alternatively you can also press Ctrl + A inside a text box when you are typing.)
2. Right mouse button click on highlighted text
3. In the menu click on "Check with DupeOff..."
DupeOff checks duplicate content and plagiarism issues and gives you a nice report.