While working on a project, I came across an interesting bug in the Firefox rendering engine involving html comments. As it turns out, it's likely related to a very old "bug" that has roots in the folks over at Mozilla following the SGML specs quite strictly. However, I think this particular implementation deserves posting due to its brevity as well as its oddity.

Firefox users will see a nice message inside the modal window, while other browsers will not. How was this accomplished? Take a look:

<!-- >If you can see this you are using Firefox!<!-- -->

Update: it appears IE will render the following as well:

<!-->If you can see this you are using Firefox or IE!<!-- -->