This is a pretty cool little add-on to use with Firefox. It helps you manage PDF files that you are download and helps eliminate the freezes that can be cause by that. A PDF can be converted into HTML for easier downloading and viewing.
The add-on button lets you easily convert a web page into a PDF or have it emailed to you as a PDF.
It looks like it's in partnership with Nitro PDF.
I find it's a handy little button to have and it looks like they also have a version for people who are using the Flock browser as well.
Firefox PDF Download Add-On:
https://addons.mozilla.org/en-US/firefox/addon/636