Load HTML in Firefox Extension

I want to create a Firefox Extension which will display a webpage. It will be like user should write a something in browser like "about:" or even a button would do ? How can i load the WebPage in Firefox. The user should have a feel that a webpage is being loaded.

PS: I have javascript and CSS in that Page.

If i cannot make then what changes do i need to make in the web page for that change.

I also want to connect to a server and fetch XML data and want to display process that data and and display it on the page. I am developing this extension as my page is static and HTML/开发者_如何转开发Javascript does not allow cross domain queries. I hope that cross-domain queries are possible if i use extension.

There is Browser XUL object that acts a an standalone browser. You can load any document inside that.