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Revision as of 11:28, 24 February 2013 by Rob W (talk | contribs) (Mentioned limit of integers (a real-life scenario is when the developer attempts to save timestamps as in
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This method allows user script authors to persist simple values across page-loads.

Strings, booleans, and integers are currently the only allowed data types. Values are saved in the Firefox preferences back end and can be manually inspected or changed by typing about:config in the address bar and searching for the preference name "greasemonkey.scriptvals.namespace/script_name.value_name". (For appropriate values of namespace, script_name and value_name.)

The Firefox preference store is not designed for storing large amounts of data. There are no hard limits, but very large amounts of data may cause Firefox to consume more memory and/or run more slowly. [1] Integer preferences must be in the range -231-1 to 231-1. Numbers outside this range can be stored by using .toString() before GM_setValue. [2]

Compatibility: Greasemonkey 0.3b+


function GM_setValue( name, value )


String The unique (within this script) name for this value. Should be restricted to valid Javascript identifier characters.
String, Integer or Boolean Any valid value of these types. Any other type may cause undefined behavior, including crashes.




Set the name foo to hold the value bar:

GM_setValue("foo", "bar");

See Also


  1. Please see this mailing list thread for details.
  2. "Note: Preferences cannot store non-integer numbers or numbers outside the signed 32-bit range -(2^31-1) to 2^31-1, If you have such a number, store it as a string by calling toString() on the number before passing it to this method" source code on Github