Again, downloading files does not work. But this time, it's more serious: When following an url that
points to a file, the browser crashes. Thus downloads are impossible.

The problem arises with the newest version of firefox: 47.0. Regretfully, the behavior is the same when
replacing firefox with palemoon. Otherwise, I use archlinux and conkeror-git 160130.1.20.g9f2b548-1.
There is no message in the console.

Any help would definitely be appreciated.

The problem is that the mime types of files that are to be downloaded are not detected correctly.

E.g., a pdf file can be downloaded with the "save" command, but the file name gets the extension "html".
Also the "shell-command-on-file" works, you may type in a pdf viewer manually. Hence it seems that when
following a link to a pdf file, conkeror assumes it is a html page, tries to display it as a webpage, and
crashes.

Anybody knows how conkeror determines the mime types? Maybe some external program or service is used for
this purpose?

I cannot replicate this. I'm using archlinux, firefox 47.0.1-1, and conkeror-git 1.0.3.r11.g66bcc3f-1.

With the default configuration (i.e., no .conkerorrc) saving and opening pdf files with external programs
works just fine.

Conkeror uses firefox's mimeservice api to determine mime types:

https://dxr.mozilla.org/mozilla-beta/source/netwerk/mime/nsIMIMEService.idl

AFAICT, that hasn't been changed recently.

The case remains completely mysterious ...

My configuration is exactly the same (archlinux, firefox 47.0.1-1, and conkeror-git
1.0.3.r11.g66bcc3f-1), I do not use any .conkerorrc, and I start without the .conkeror.mozdev.org
directory. To repeat the story with a specific example: I visit http://arxiv.org/abs/1604.06973, I click
on the link "PDF", which points to the pdf-file http://arxiv.org/pdf/1604.06973v1, and conkeror crashes.
I may instead press "s" ("save"), choose that same pdf-file, and download it -- and its name will be
"1604.html". The erroneous extension "html" is of course added by the browser.

Always downloading a file instead of following the link to it is, unfortunately, no solution. For
instance, when visiting pages with an embedded pdf, conkeror used to show a black area where the pdf is
supposed to be shown, now it crashes immediately when I visit such a page.

Thanks anyhow for the feedback. I guess I will not find out what the problem is, it has occurred since a
couple of days, after a usual upgrade of the system, which included firefox but not conkeror. But as
noticed already, the upgrade of firefox is not likely to be the problem, I have the same behaviour with
firefox 45 and with palemoon.

Luckily, I finally found the solution. The problem is related to the so-called plugin container. Firefox
had activated a plugin named evince. I simply deactivated it, and everything works as usual.

The annoying point about this: I never installed any plugin for firefox / conkeror other than flash and
vlc. The reason of the above described problems was apparently that, some time ago, I installed evince.
In the sequel, firefox activated the evince plugin. This might have happened when I once tried to open a
ps file under firefox (not conkeror).

I guess this is not a bug of conkeror, but of firefox as well as of palemoon. In firefox, the "evince
plugin" does not work for me either, trying to open a ps file leads to a crash. For palemoon, the same
issue as discussed here is described at https://bbs.archlinux.org/viewtopic.php?id=214285.