Category:Coding Tips:Interacting With The Page
The Greasemonkey sandbox, with its use of XPCNativeWrappers guarantees the security of the advanced capabilities a user script has from the potentially malicious content page. However, it does introduce a number of restrictions that can be difficult to understand. Also, this security is guaranteed only if the script does not break the security model; dangerous tools like unsafeWindow are provided to authors in the rare case that it is the only possible method.
It's rare that unsafeWindow is the only method, however. These pages detail a variety of approaches that can make it easier to interact with the content page, when Greasemonkey's security model might otherwise get in the way, without compromising security.