unsafeWindow

This command can open certain security holes in your user script, and it is recommended to use this command sparingly.

Please be sure to read the entire article and understand it before using it in a script.

Well, there are certain techniques

Examples

unsafeWindow.SomeVarInPage = "Testing";

unsafeWindow.SomeFunctionInPage("Test");

var oldFunction = unsafeWindow.SomeFunctionInPage;
unsafeWindow.SomeFunctionInPage = function(text) {
  alert('Hijacked! Argument was ' + text + '.');
  return oldFunction(text);
};

Alternatives to unsafeWindow

Sometimes, you just can't get around using unsafeWindow. Most of the time, however, you can! See Category:Coding Tips:Interacting With The Page for details on various methods to interact with the page that do not use unsafeWindow.

Notes

BUG: In Firefox 3.0 the prototype field will always be undefined for objects accessed through unsafeWindow. The techniques in Category:Coding Tips:Interacting With The Page can work around this problem.