Firefox 19 comes with a built-in PDF viewer. It looks like this:
![PDF viewer in Firefox](https://winaero.com/blog/wp-content/uploads/2013/02/PDFinFirefox1-600x484.png)
Although I like this new feature, because it works fast and looks smooth, you might want to disable it for whatever reason (for example, if the full PDF is not rendered perfectly) . Read below to see how.