This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
Prints messages to the (native) console.
messageis the string message to log.
A common use of
dump() is sent to the System Console (Native Console) if the Firefox process was started with the
-console option. If the
-console option was not specified then the output goes to stderr. Output from dump() is not sent to the Browser Console. Output can be sent to the Browser Console using console.log(). Privileged code can also use
nsIConsoleService to log messages to the Error Console/Browser Console.
window is not the global object in components. It is also explicitly made available in sandboxes. However, this use of
dump is not affected by the preference mentioned below -- it will always be shown. It is therefore advisable to either check this preference yourself or use a debugging preference of your own to make sure you don't send lots of debugging content to a user's console when they might not be interested in it at all. Note that
dump output from XPCOM components goes to
dump called elsewhere will output to
dump() is disabled by default – it doesn't do anything but doesn't raise an error either. To see the
dump output you have to enable it by setting the preference
true. You can set the preference in about:config or in a user.js file. Note: this preference is not listed in
about:config by default, you may need to create it (right-click the content area -> New -> Boolean).
On Windows, you will need a console to actually see anything. If you don't have one already, closing the application and re-opening it with the command line parameter
-console should create the console or use
-attach-console to use the existing console. On other operating systems, it's enough to launch the application from a terminal.
To redirect the console output to a file, run firefox without the -console option and use the syntax to redirect stderr and stdout to a file, i.e.:
firefox > console.txt 2>&1
If you would like the console messages to appear in the console you used to launch the application, you can use the Gecko Console Redirector. Precompiled binaries are available in the zipped archive https://github.com/matthewkastor/Redirector/archive/master.zip under
Redirector-master\Gecko\Console Redirector\bin\Release Copy all the dll's and the exe to wherever you want. Then run
Console Redirector.exe /?
This is not part of any specification