Firefox users have been using the built-in PDF viewer for a long time now. We should add PDF files to the list of files we can handle as the default browser. In Windows 10 right now the only browser that seems to do this is Edge. As a Firefox user, I was surprised to click on a pdf file and have it open in Edge instead of Firefox.

I seem to recall this having come up before, but can't find the bug. The tricky question was that, AIUI, the Firefox PDF viewer was originally just trying to just be an acceptable enough PDF viewer to lessen the need to install 3rd party PDF software (due to malware or security issues), since PDFs are so commonly used on the Web. But it wasn't a goal to handle everything, and we were happy to let the OS or the 3rd party software deal with that. Worth looking at again, especially since on Win10 it's just opening in Edge. Do we know how well Edge's PDF renderer compares to PDF.js?

It's interesting - on Windows XP, older versions of Firefox would take over as the default viewer if no other was installed. Maybe that needs to be brought back? What happens if you take a PDF, right-click it, and Open With, manually browse to the FF binary? Does it just prompt you with a download or does it open?

(In reply to Alan Xenos from comment #2) > It's interesting - on Windows XP, older versions of Firefox would take over > as the default viewer if no other was installed. Maybe that needs to be > brought back? What happens if you take a PDF, right-click it, and Open With, > manually browse to the FF binary? Does it just prompt you with a download or > does it open? I don't know what happens on XP but in Windows 10 if you right-click on a PDF, Firefox isn't one of the options that you can choose from. You have to choose to see more options and then choose "some other software on your computer", then pick Firefox which adds it to the menu. Then if you choose Firefox *again* the pdf just opens up in a tab like you'd expect. I guess the main question is what Dolske asks in comment 1: > Do we know how well Edge's PDF renderer compares to PDF.js? I don't have an answer for that.

Bug 1197191 should have fixed this. Note that "Default Programs" control panel applet or "Default apps" setting will not set Firefox as the default .pdf handler ("Default apps" will not set Edge either when selecting the default "Web browser"). But "Open With" context menu item will list Firefox as a .pdf handler. If no .pdf handlers exist (e.g. on WinXP without Adobe Reader or any other third-party .pdf viewers installed), Firefox will take the default.