1. Download and install Joliprint firefox add-on from here.
2. After installing and restarting Firefox, now you will get a icon of printer as shown in image below.
3. Now go to the webpage that you want to save as PDF file.
4. Click on that icon. You can also do this by right click on the webpage that you want to convert you can press a shortcut key Ctrl+Alt+P Now you can see a new popup will shown on Firefox screen.
5. Once the webpage is converted you will see screen like this. Now you can easily download your converted PDF by clicking on “Download your PDF” or you can share your converted PDF with your friends on Facebook. You can also tweet this by clicking on twitter icon.
Source: http://www.techwallz.com/joliprint-convert-webpages-pdf-files-easily/