The message manager

The message manager is a message-passing framework for chrome script to touch content. In Firefox 4, chrome script can access content and content docshells directly through properties on a XUL browser element. But in Mobile Firefox 4 and in a future version of Firefox, content will run in separate processes from chrome, and direct access will not be possible. Instead, chrome script must use separate scripts for code which must synchronously touch content, and run these scripts asynchronously using the message manager. The message manager is available in Firefox 4 so that Firefox code and extensions can start using the new API immediately, even before Firefox switches to use content processes. https://wiki.mozilla.org/More samples and docs here: Mobile/Fennec/Extensions/Electrolysis