1. Mozilla says another instance is already running, but there is none

Try making a new profile, and using it instead:

conkeror -no-remote -ProfileManager

Further details: http://kb.mozillazine.org/Profile_in_use#Check_the_profile_folder_name_and_location

2. Conkeror fails to start, and there is no error message of any kind

This can be caused by a corrupt or out-of-date profile. Delete your ~/.conkeror.mozdev.org/ directory.

This can also be caused by certain Mozilla errors that happen early enough during initialization, before Conkeror proper has been loaded, so they are not caught and dumped to the terminal. To see if such errors are present, start conkeror with the -jsconsole flag.

3. Error spawning process: conkeror-spawn-helper not found; try running "make"

In order to use external editing, you need conkeror's conkeror-spawn-helper installed. If you installed conkeror manually, you just need to run make in its base directory. If you installed conkeror from your operating system, there is likely a package available for conkeror-spawn-helper. In Debian and Ubuntu for example, you need to install the package conkeror-spawn-process-helper.

4. When downloading something, both the Conkeror download manager and the Mozilla download manager pop up

This is a problem having to do with XPCOM registration. Delete the following files from your profile directory so they can be automatically recreated: xpti.data, compreg.dat, XPC.mfasl.

5. Conkeror always starts in offline mode

This problem may appear in Debian systems and a workaround for it consists in removing the network-manager package. Alternatively adding the following to your .conkerorrc will also avoid it:

io_service.manageOfflineStatus = false;
io_service.offline = false;

Also note the interactive commands:

network-go-online
network-go-offline

6. Limitations of MIME type overriding

The view-as-mime-type command (bound to v by default) as well as the "view internally" and "view as text" options in the download prompt depend on a facility in Conkeror known as MIME type overriding. Unfortunately, this facility is implemented in a somewhat hacky way, due largely to limitations in Mozilla, and as a result has the following limitations:

• Only HTTP and HTTPS URLs are supported
• In some cases the MIME type that Mozilla guesses from the content stream (so-called content sniffing) will take precedence over any override MIME type that is specified. Fortunately, I believe in all such cases the internal viewer (Gecko) will not be able to handle the content usefully anyway.
• The URL will be re-requested from the server (any cached version will be discarded), and the resulting content will be stored in the cache with the overridden MIME type.
• If the "view internally" or "view as text" options are used from the download prompt, the existing request will be aborted and a new GET request for the same URL will be generated. Consequently, these download options will probably not work correctly for POST requests.

7. Shift-insert does not work when the primary selection was set by the xclip program

There seems to be a problem in mozilla, or possibly xclip, such that mozilla doesn't see data that xclip places in the primary selection buffer. The work-around is to use xsel instead of xclip, if possible.

If you use xclip.el in emacs, you can override the function xclip-set-selection with the following version, to set the selection with xsel instead of xclip:

(defun xclip-set-selection (type data)
  "TYPE is a symbol: primary, secondary and clipboard.

Use xsel instead of xclip.  Just a hack.

See `x-set-selection'."
  (when (and xclip-program (getenv "DISPLAY"))
    (let* ((process-connection-type nil)
           (proc (start-process "xclip" nil "xsel" "-i"
                                (if (eq type 'clipboard) "-b" "-p"))))
      (process-send-string proc data)
      (process-send-eof proc))))

8. Conkeror fails to run external program on finished download

For a possible explanation see Issue 114. The upshot of the discussion there is that changing the value of browser.download.manager.retention to 1 or 2 may resolve the problem. See this page for details of this preference.