Change Firefox settings from addon

Hello I have not created a Firefox addon before and I would be grateful for any ones feedback about why the following code is not changing the Default Home Page setting when I have installed my addon.

defaultPref(“browser.startup.homepage”, “www.bing.com.au”);

I have also tried -
defaultPref, lockPref, Pref, User_Pref
lockPref(“browser.startup.homepage”, “data:text/plain,browser.startup.homepage=www.bing.com.au/”);
lockPref(“browser.startup.homepage;www.bing.com.au”);

There are various ways to change preferences from an add-on. Check out the docs for more information.