Take a look at some of the docs for opening URLs in new Tabs and manipulating the content of the tab:
https://developer.mozilla.org/en/Code_snippets/Tabbed_browser#Opening_a_URL_in_a_new_tab
Once you get comfortable with that, try opening an HTML page that lives in your add-on. First, you need to be aware of the 'content' package name you registered in your chrome.manifest file. Second, make sure your 'domains.html' file is in the content folder of your add-on. To open the web page in a new tab using a button or menu in Firefox use code like this:
gBrowser.addTab("chrome://mypackagename/content/domains.html");
You can should be able to load other JS and CSS files from your add-on into the web page using similar chrome:// URIs.