Combine PDF Files, Convert Web Page URLs to PDFs on the fly
LOOP is a unique extension for Firefox that converts the web browser into a proper PDF writer that can do some amazing things sometime not possible in other free PDF conversion software.
First and foremost, as you are browsing the web, click the Add URL button and that webpage will be converted to PDF almost immediately - the entire process requires a single click. You can continue browsing and keep adding more URLs to the PDF queue - all the PDF conversions will happen in the background with interrupting your work.
If you have any local documents (like Word, Powerpoint, Excel or Images), LOOP for Firefox will convert those as well to PDF files - click the "add file" button.
And finally, there's a "Combine All" button which will merge all the PDFs that you added to the queue and will create one PDF file out of them. You can also reorder the pages in the Combined PDF with the "move up" or "move down" buttons.
Pretty innovative and useful extension. Requires you to create a quick account on Drawloop website. The pro version offers password protected PDFs.
LOOP for Firefox | User Manual