Refer to this article: Firefox Comment Rendering, It's Not A Bug! But We'll Fix It
This page demonstrates a bug in Firefox that renders comments incorrectly. Except that it's not incorrect according to the specs for HTML4 and below. Here's how it goes. There is a comment after this paragraph surrounded by [ ]. It contains a double hyphen (--) without a closing ">".[ ] You should see nothing before this sentence.
Let's see what happens. What the hell is that "-->" doing there?
What about a single line comment? [ ] You should see nothing before this sentence.