This Firefox extension toggles the mozTCPSocket, mozContacts, mozbrowser, Notification APIs and systemXHR for web pages in Firefox, so you can test Open Web Apps that need access to those APIs in the browser.
Install it, then press the "Plug-In" button in your toolbar while the page in question is loaded into the active tab, and the extension will enable those APIs for that page. Press the button again to disable those APIs.
The APIs will remain enabled across page reloads, browser sessions, and even after you uninstall the extension! So make sure you disable them once you no longer need to test the page. And be careful about the pages for which you enable the APIs, since you're escalating their privileges!
"Plug-In" icon designed by Florian Huber from the Noun Project.