There are a couple of preferences associated with the Gecko remote protocol:


Starts and stops the Marionette server. This will cause a TCP server to bind to the port defined by marionette.port.

If Gecko has not been started with the -marionette flag or the MOZ_MARIONETTE environment variable, changing this preference will have no effect. For Marionette to be enabled, either one of these options must be given to Firefox or Fennec for Marionette to start.


Delay server startup until a modal dialogue has been clicked to allow time for user to set breakpoints in the Browser Toolbox.


Sets the verbosity level of the Marionette logger repository. Note that this preference does not control the verbosity of other loggers used in Firefox or Fennec.

The available levels are, in descending order of severity, Trace, debug, config, info, warn, error, and fatal. The value is treated case-insensitively.


Certain log messages that are known to be long, such as wire protocol dumps, are truncated. This preference causes them not to be truncated.


Defines the port on which the Marionette server will listen. Defaults to port 2828.

This can be set to 0 to have the system atomically allocate a free port, which can be useful when running multiple Marionette servers on the same system. The effective port is written to the user preference file when the server has started and is also logged to stdout.


Used internally in Marionette for determining whether content scripts can safely be reused. Should not be tweaked manually.

This preference is scheduled for removal.