Command Line Parameters

Firefox recognizes many (many!) command line parameters. Overview documentation of these parameters lives here.

Most parameters can be supplied with either a single dash (-foo) or a double dash (--foo); the two forms are equivalent. Many parameters are registered by individual components, so the exact set available depends on the build and platform. A current list can always be printed with firefox --help.

Startup and profiles

Parameter	Description
-h, --help	Print a usage message listing the available parameters and exit.
-v, --version	Print the Firefox version and exit.
--full-version	Print the Firefox version together with the build and platform build ids and exit.
-P <profile>	Start with the named <profile>.
--profile <path>	Start with the profile located at <path>.
--migration	Start with the migration wizard.
--ProfileManager	Start with the Profile Manager.
--new-instance	Open a new instance rather than a new window in an already running instance.
--no-remote	Do not accept or send remote commands; implies --new-instance.
--safe-mode	Disable extensions and themes for this session.
--allow-downgrade	Allow a profile created by a newer version of Firefox to be opened by an older version (only available on builds that block profile downgrades).
--first-startup	Run post-install actions before opening a new window.

Opening content

Parameter	Description
--browser	Open a browser window.
-url <url>	Open <url>. This is the parameter implicitly used when a bare URL is passed on the command line, and the one used when another application delegates a URL to Firefox.
--new-window <url>	Open <url> in a new window.
--new-tab <url>	Open <url> in a new tab.
--private-window [<url>]	Open <url> (or a blank page) in a new private window.
--search <term>	Search for <term> with the default search engine.
--preferences	Open the Preferences (Options on Windows) dialog.
--setDefaultBrowser	Set Firefox as the default browser.

Display modes

Parameter	Description
--headless	Run without a GUI. Available on Windows, Linux (GTK) and macOS.
--screenshot [<path>]	Take a screenshot and save it to <path> (or to the working directory). Implies --headless.
--window-size width[,height]	Width and, optionally, height to use for --screenshot.
--kiosk	Start the browser in kiosk mode.
--kiosk-monitor <num>	Place the kiosk browser window on the given monitor.
--disable-pinch	Disable touch-screen and touch-pad pinch gestures.

Logging and debugging

Parameter	Description
--MOZ_LOG=<modules>	Treated as the MOZ_LOG=<modules> environment variable, overriding it.
--MOZ_LOG_FILE=<file>	Treated as the MOZ_LOG_FILE=<file> environment variable, overriding it. If neither this argument nor the environment variable is set, logging is written to stdout.
--jsconsole	Open the Browser Console.
--devtools	Open the DevTools on initial load.
--jsdebugger [<path>]	Open the Browser Toolbox. Defaults to the local build but can be overridden by a Firefox path.
--wait-for-jsdebugger	Spin the event loop until the JS debugger connects, enabling debugging of (some) application startup code paths. Only has an effect when --jsdebugger is also supplied.
--start-debugger-server [ws:][ <port> | <path> ]	Start the DevTools server on a TCP port or Unix domain socket path. Defaults to TCP port 6000. Use the WebSocket protocol if the ws: prefix is specified.
--marionette	Enable the remote control (Marionette) server.
--origin-to-force-quic-on <origin>	Force the use of QUIC for the specified origin.

Platform-specific parameters

Parameter	Description
--console	On Windows, start Firefox with a debugging console.
--dbus-service <launcher>	On Linux builds with DBus support, run as a DBus service for org.freedesktop.Application and set <launcher> (usually the /usr/bin/appname script) for it.
--display=DISPLAY	On X11, the X display to use.
--sync	On X11, make X calls synchronous.
--g-fatal-warnings	On Unix, make all warnings fatal.
-osint	On Windows, -osint serves two purposes. Most importantly, it signals that the command line is untrusted and must be sanitized. Command lines with -osint are rejected unless they have a very specific structure, usually firefox.exe -osint -url URL or firefox.exe -osint -private-window URL: refer to the EnsureCommandLineSafe function. These command lines are produced by apps delegating to Firefox, and the resulting URL may not be correctly quoted. The sanitization process ensures that maliciously chosen URLs do not add additional parameters to Firefox. Secondarily, the -osint parameter signals that Firefox is being invoked by Windows to handle a URL: generally a registered file type, e.g., .html, or protocol, e.g., https.