While most PDF files can be viewed directly in the browser, some PDFs will trigger a "Save as"-dialog or will be downloaded automatically. This addon views all PDF files directly in the browser. You can still save the PDF by pressing Ctrl+S (or Cmd+S) after viewing them. Please make sure that the setting under "Firefox > Preferences > Applications > PDF" is set to "Preview in Firefox" in order for this addon to work. Some web servers are misconfigured and do not tell the browser that a file is a PDF. In this case the file will still be downloaded even when this addon is active. If this happens, you can report it as a potential issue on the linked support page (GitHub). Changes from the original extension version:

• Properly support more sites:
  • Dropbox
  • Google Docs "Print" functionality and other products.
  • Amazon cloud
  • itch.io
  • various universities
• Allow forcing downloads and disabling the extension by clicking on the browser action icon.

Permissions:

• Requires the "Access your data for all websites" because it needs to check if any request is potentially a PDF (and in that case modify it to prevent it from being downloaded).