Not displaying PDF in web browser should deregister plug-in

[VanguardLH]

When installing PDFXchange Viewer, it registers its plug-in (npPDFXCviewNPPlugin.dll) for Firefox under the following registry keys:

• HKEY_CURRENT_USER\Software\MozillaPlugins\@docu-track.com/PDF-XChange Viewer Plugin,version=1.0,application/pdf
• HKEY_LOCAL_MACHINE\SOFTWARE\MozillaPlugins\@docu-track.com/PDF-XChange Viewer Plugin,version=1.0,application/pdf
• HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\MozillaPlugins\@docu-track.com/PDF-XChange Viewer Plugin,version=1.0,application/pdf

If the user configures PDFXchange Viewer to not display PDFs inside the web browser then this plug-in does not need to be registered. In the Applications configuration of Firefox, the user can elect which external program is the handler for .pdf filetypes to open them outside of the web browser.

If you visit https://panopticlick.eff.org/ and run the test, you will see that querying the web browser for a list of its plug-ins is one method of fingerprinting a user. While Adobe Reader is very common (probably the most used PDF viewer), PDFxchange Viewer (or PDFxchange Editor) are far fewer in number of users which means anyone using PDFxchange <whatever> will have a bigger fingerprint. When the user configures PDFxchange Viewer to not display PDFs within the web browser, the plug-in is not used so it does not need to be registered which exposes it through the web browser to sites that query what plug-ins are available.

Display PDFs in web browser = enable: use the plug-in (so register it when enabling this option)
Display PDFs in web browser = disable: don't use the plug-in (so deregister it when disabling this option)

I realize the old scheme was to register a plug-in even if it is not used. The author provides a plug-in and expects users want to use it. However, if users elect to display PDFs outside the web browser then the plug-in is superfluous and so is its registration in the registry as a plug-in to the web browser.

If PDFxchange Editor works the same way then this request (to deregister the plug-in when "Display PDF in web browser" is disabled) also applies.

[Stefan - PDF-XChange]

Hello VanguardLH,

Thanks for the detailed post above. I am afraid that the Viewer is at it's end of life, so it's unlikely we will change the behaviour for it - especially when browsers are now closing support for external plug-ins with moving away from NPAPI - but I will check with the devs how is the Editor plug-in registered and if we can do the changes you suggest above.

Regards,
Stefan