Hi,

Beginning with Firefox version 52, support has ended for all NPAPI plugins except for Adobe Flash.

So you cannot open the PDF inside of Firefox. You should use the following link to setup Firefox so you can open the PDF in a separate PDF window and not within the browser.

https://support.mozilla.org/en-US/kb/use-adobe-reader-view-pdf-files-firefox#w_viewing-pdf-files-in-firefox

Please reply if this helps or whether we can further assist you.

ffoxed said

From first installation of Quantum (Refresh, no add-ons) it goes bananas if I click on a pdf link. I have of course disabled default open in Ff for saved pdfs, and removed Foxy, which purported to save pages as pdf.

Sorry so late back. I suppose the main thing to report back is that you can in fact open PDFs inside of Ff, since Preview in Firefox under Options effectively does that, but I cannot work out what has still occasionally been causing that setting to malfunction. Not any add-ons apparently.

Thank you for your link. There are references to "built-in" handling of pdfs all over Support, but there was certainly nothing like that built into vsn 57 when I first installed it, and pdfs pf whatever source or in whatever form simply precipitated manic opening of about:blank tabs, I think because of a previous setting to Open in Ff rather than Preview in Ff, and the multiple firefox.exes in Task Manager had to be shut down one at a time faster than they loaded! (These multiple firefox.exes persist since the pdf problem has resolved. Are they a feature of Quantum?) I defeated the setting "reopen tabs from last time" eventually before I could do anything in Options.

I certainly would not want to open pdfs in a separate pdf window, still less in Acrobat, which I had long since uninstalled, when all I had to do was set Options to Preview in Ff (and hope it stayed functional).

I concluded this was the built-in functionality which was supposed to be in place for 57, and that 57 was but half made up when it was released!

It was described as having been rebuilt "from the bottom up". To me this always suggests inductive reasoning at the expensive of top-down functional thinking. I wonder if such improvements as I have witnessed to the initially dodgy functionality have had more to do with hypothetico-deductive thinking since that release!

If you ever see a download dialog for a file (PDF or other) and it asks you what application you want to use to open it, please don't select Firefox. Firefox would have already opened the download in that case. It is safer to save it to disk and then open it from disk if you think Firefox can handle it. Otherwise, this can happen: Firefox repeatedly opens empty tabs or windows after you click on a link.

Gosh, an almost instantaneous reply. Thank you. I've given it some thought and experimentation, but I'm still puzzled. Are you saying some varieties of pdf prompt this dialogue and not others? I only ever saw any such dialogue when I had set pdf handling to Always Ask in Options, and I'm only too glad to have been able to avoid it by resetting to Preview in Ff. I can still choose to save or open in a separate program.

Or are you saying it's hazardous even to use the Preview option? If so why is it there? And why do these multiple windows or tabs only get triggered in this version? I don't think it happened before. Is it something to do with this new proliferation of firefox.exes in taskman, which are not a feature which inspires confidence in the "lightning-fast" claim. The speed seems as vulnerable to resource-hoggery as ever.

ffoxed said

Are you saying some varieties of pdf prompt this dialogue and not others?

No, this is an issue with the Content-Type indicated by the server, not the actual file itself. If the server sends "application/pdf" Firefox will default to using the built-in viewer. If the server sends some other content type that doesn't have a preexisting association, you'll get a download dialog. This is not always apparent from the dialog; you would have to dig into the developer tools to see what headers were sent with the file.

Or are you saying it's hazardous even to use the Preview option?

No, I'm definitely not saying that.

And why do these multiple windows or tabs only get triggered in this version?

It's not a new issue, but the data file that stores download handlers changed recently, perhaps in Firefox 56, and there may have been a glitch in the conversion.

Is it something to do with this new proliferation of firefox.exes in taskman, which are not a feature which inspires confidence in the "lightning-fast" claim. The speed seems as vulnerable to resource-hoggery as ever.

To manage the number of processes, see: Firefox's performance settings.