ubuntu 12.04
conkeror nightly build (wheezy) 1.0~~pre+git1312132307-~nightly1
firefox 26.0+build2-0ubuntu0.12.04.2

Before the latest updates (yesterday) conkeror would work without problem.

Now I get the following errors:

$ conkeror
xulrunner not found, trying firefox instead.
Error initializing.
NS_ERROR_UNEXPECTED: Component returned failure code: 0x8000ffff (NS_ERROR_UNEXPECTED)
[nsIDownloadManager.addListener]
null()@chrome://conkeror/content/download-manager.js:383
load1()@file:///usr/share/conkeror/components/application.js:108
application.prototype.load()@file:///usr/share/conkeror/components/application.js:160
application.prototype.require()@file:///usr/share/conkeror/components/application.js:231
null()@chrome://conkeror/content/conkeror.js:47
load1()@file:///usr/share/conkeror/components/application.js:108
application.prototype.load()@file:///usr/share/conkeror/components/application.js:160
application.prototype.require()@file:///usr/share/conkeror/components/application.js:231
application()@file:///usr/share/conkeror/components/application.js:40
null()@resource://gre/modules/XPCOMUtils.jsm:271
cmdline.prototype.handle()@file:///usr/share/conkeror/components/command-line.js:20
null()@null:0
************************************************************
* Call to xpconnect wrapped JSObject produced this error:  *
[Exception... "'[JavaScript Error: "conkeror.handle_command_line is not a function" {file:
"file:///usr/share/conkeror/components/command-line.js" line: 23}]' when calling method:
[nsICommandLineHandler::handle]"  nsresult: "0x80570021 (NS_ERROR_XPC_JAVASCRIPT_ERROR_WITH_DETAILS)" 
location: "native frame :: <unknown filename> :: <TOP_LEVEL> :: line 0"  data: yes]
************************************************************
Console error: [JavaScript Error: "conkeror.handle_command_line is not a function" {file:
"file:///usr/share/conkeror/components/command-line.js" line: 23}]
  Category: XPConnect JavaScript

If I should add any information, please let me know

Does Firefox 25 work?

firefox_25.0.1+build1-0ubuntu0.12.04.1 was working

I installed now Mozilla XULRunner 26.0 - 20131205075310

Using simply the command "conkeror" gives the same error as befor.

But I can now run it without any error message with xulrunner /usr/share/conkeror/application.ini

The cause of the problem seems to be that nsIDownloadManager has been deprecated as of Firefox 26.

https://developer.mozilla.org/en-US/docs/XPCOM_Interface_Reference/nsIDownloadManager?redirectlocale=en-US&redirectslug=nsIDownloadManager

If we want to support Firefox 26 and higher as a platform, things that use nsIDownloadManager and
nsIDownload will need to be changed to use Downloads.jsm when those interfaces are not available.
(Will need to support both, for sake of compatibility with older versions as well.)

Just by way of confirmation: the update to Firefox 26 stopped conkeror from launching with exactly the
same console output provided by quantum.  Installing 'Mozilla XULRunner 26.0 - 20131205075310' seems to
have fixed the problem as well.

Details: 
Ubuntu 12.10, 64 bit

$ firefox -v
Mozilla Firefox 26.0

$ conkeror -v
xulrunner not found, trying firefox instead. 
conkeror.mozdev.org conkeror 1.0pre (Debian-1.0~~pre+git1312212307-~nightly1)

$ conkeror
[output as described by quantum above]

And (now) this works:

$ xulrunner -v
Mozilla XULRunner 26.0 - 20131205075310

$ xulrunner /usr/share/conkeror/application.ini

Just confirmation: I also have this on Gentoo Linux and there is an appropriate bug on its bugzilla:
https://bugs.gentoo.org/show_bug.cgi?id=497024

The gecko26-downloads-fix branch resolves this.  The branch will hopefully be merged to master soon, and
I am using it myself, but any additional testing would be great.

@jbms

Thank you. I've tested your fix, it works well for me.

Support is now in master branch.