The meta key is used in many key combos, and it is vital to the keyboard UI of Conkeror. However, not all keyboards have a meta key. Therefore Conkeror takes a guess whether your keyboard has a meta key, based on the operating system you are using. The Command key on a Mac is a meta key, so if you are running Conkeror on OS X, your Command key will be what Conkeror considers as meta. If you are running on any other operating system, Conkeror will treat your Alt key as a meta key.

If your keyboard has a meta key, but since you are not in OS X, Conkeror uses your Alt key instead, you can configure Conkeror to use your meta key by putting the following in your rc script:

modifiers.M = new modifier(
    function (event) { return event.metaKey; },
    function (event) { event.metaKey = true; });

Note that due GTK2, if you have used xmodmap to add a meta key, it should be mod4.

Additionally, you can add a modifier A for Alt as follows. The variable modifier_order must be set before any calls to define_key.

modifier_order = ['C', 'M', 'A', 'S'];