Question

I am learning to create addons for Firefox and I have a question about xul. I want to know if it is possible to add xul elements to all any webpage I go on (not the tab/tool/menu bar).

I want to be able to put something like a div (box) on the webpage separate from the dom of the page (because I would like it to appear there even if I change webpages). It is not a popup (I do not want it in its own window) but an element on the page. I know i can load up JavaScript to edit the page (similar to Greasemonkey userscripts) but I would like it to not load up every time I go to a new page.

If you need more information I can provide some more. Thanks in advance.

Answer 1

No, this is not possible. XUL is a language created by Mozilla for creating the application that houses your HTML code:

Mozilla has configurable, downloadable
chrome, meaning that the arrangement
and even presence or absence of
controls in the main window is not
hardwired into the application, but
loaded from a separate UI description.
In fact, most of Mozilla’s windows
(and dialogs) will be described using
this mechanism. XUL (pronounced
“zool,” as if that spelling helped
any, and short for “XML User Interface
Language”) is our name for the
language in which these UI
descriptions are built.

Window chrome is displayed and managed
by the same layout engine that manages
HTML content in the browser. UI
descriptions, then, look a great deal
like HTML 4. XUL is an application of
XML. In fact, it is just XML with
specific meaning defined for a few
element types, and into which HTML can
be scattered.

(source)

It is used to build applications that contain web browsers, and is extensible to allow it to include HTML code in the xul application, but it is not possible to do the opposite, since the HTML language doesn’t recognize XUL code.

Simply put, your HTML code is in an HTML browser embedded in the XUL-coded application (firefox). Two different languages, for two different purposes. If you want XUL-like elements in your HTML, you will have to use css to create them, but you can’t embed XUL in HTML.