This method allows user script authors to persist simple values across page-loads.
Strings, booleans, and integers are currently the only allowed data types.
Per Greasemonkey 1.13+ values are saved per userscript in a SQLite database. You can find the corresponding database by the userscript
basedir as defined in the
config.xml. The values are only accessible by opening the database is an SQLite reader, like add-on SQLite Manager.
In older Greasemonkey version, 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 "
(For appropriate values of
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. 
Integer preferences must be in the range -231-1 to 231-1. Numbers outside this range can be stored by using
Compatibility: Greasemonkey 0.3b+
function GM_setValue( name, value )
BooleanAny valid value of these types. Any other type may cause undefined behavior, including crashes.
Set the name foo to hold the value bar:
- Please see this mailing list thread for details.
- "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