Having multiple versions of XULRunner installed on one machine is simpler than you might imagine.  If for whatever reason, you want to run Conkeror with a particular XULRunner version, you can be up and running in minutes.

== For XULRunner versions 5 and above ==

 1. Install your desired version of XULRunner and simply issue the command:
 {{{
 [xulrunner-program] [/path/to/conkeror/application.ini]
 }}}

 For example, on Debian with Conkeror version Debian-0.9.3+git110719-1 and xulrunner-7.0a2 installed from the Mozilla repositories at http://mozilla.debian.net/, the following command line was successful:
 {{{
 xulrunner-7.0 /usr/share/conkeror/application.ini
 }}}

 1. You can then make sure that your Conkeror is using the desired version of XULRunner by checking the value of `M-x version` in Conkeror.

 1. Optionally, create a convenience shell script for yourself, such as ~/bin/conkeror7, to start conkeror with the desired XULRunner version.

== For older versions of XULRunner ==

 1. download a binary archive of the XULRunner version you want, for your platform.

 1. extract it to a directory somewhere.

 1. enter that directory in a terminal.

 1. issue the command:
 {{{
./xulrunner --register-user
}}}

 1. there will now be an entry in the directory `/etc/gre.d/` for the new XULRunner version.

 1. change to your conkeror directory.  It is preferable to use Conkeror from git for this part, as not all OS-specific packages will come with the requisite scripts.

 1. issue the following command to ensure that Conkeror will be able to find the version of XULRunner that you just registered.
 {{{
./contrib/list-xulrunner-versions
}}}

 1. take note of the exact version string of the XULRunner version you want to use.  You will use this string in place of the `###` marker in the following command.
 {{{
CONKEROR_XULRUNNER_VERSION=### ./contrib/run-conkeror
}}}

 1. if all goes well, Conkeror starts, and you can verify that it used the version of XULRunner which you intended by doing `M-x version`.