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Creating toolbar buttons (Customize Toolbar Window)

This article explains how to add a toolbar button to a Toolkit application (such as Firefox, Thunderbird, or Kompozer) using overlays. Its intended audience is extension developers with a basic knowledge of XUL and CSS.

We assume that you're also familiar with the basics of creating Firefox extensions and have the Hello World extension working. Another tutorial, which walks you through the entire process from the beginning, is also available.

Creating an overlay

The first step is to create an overlay for the document containing the toolbar you wish to enhance. Explaining overlays is beyond the scope of this tutorial -- you can read about them in the XUL Tutorial.

To overlay a document, you need to know its URI. You can find a list of URIs for the most commonly overlaid documents at the bottom of this page.

Note: Some people overlay chrome://messenger/content/mailWindowOverlay.xul. that should cause the button to appear on all windows that mailWindowOverlay.xul is applied to (i.e. Main window and View Message window). This needs to be looked into.

Adding the toolbar button

Toolkit applications have customizable toolbars; therefore, it's common practice for extensions to add their toolbar buttons to the toolbar palette, rather than adding them directly to the toolbar. The latter is possible, but is not recommended and is harder to implement.

Adding a button to the toolbar palette is very easy. Just add code like this to your overlay:

<toolbarpalette id="BrowserToolbarPalette">
  <toolbarbutton id="myextension-button" class="toolbarbutton-1"
    label="&toolbarbutton.label;" tooltiptext="&toolbarbutton.tooltip;"


  • The id of the palette (BrowserToolbarPalette in the example) depends on the window (the parent window of the toolbar you wish to insert a button). See below for the list of common palette IDs.
  • class="toolbarbutton-1" makes the toolbar button appear correctly in Icons and Text mode; it also adjusts padding.
  • Set the command to be executed when the button is clicked in the oncommand attribute.
  • If you need to handle middle-click, add this line after the oncommand line.
onclick="checkForMiddleClick(this, event)"
  • you can also handle middle-click and right-click using onclick handler and check event.button in it like this:
<toolbarpalette id="BrowserToolbarPalette">
  <toolbarbutton id="myextension-button" class="toolbarbutton-1"
    label="&toolbarbutton.label;" tooltiptext="&toolbarbutton.tooltip;"
onclick: function(event) { switch(event.button) { case 0: // Left click break; case 1: // Middle click break; case 2: // Right click break; } } 

To add more buttons, put more <toolbarbutton> elements inside the <toolbarpalette> element. Wrap elements other than <toolbarbutton> in <toolbaritem>.

Adding the Button Bootstrap Style

Adding a button to the BrowserPalette on runtime in a Bootstrap addon is a bit different because the BrowserPalette is indirectly reached. A simple document.getElementById('BrowserToolbarPalette') will not work. This is the code to create and add it in.

let button = doc.createElement("toolbarbutton");
button.setAttribute("id", BUTTON_ID);
button.setAttribute("label", "Replace Bookmark");
button.setAttribute("class", "toolbarbutton-1 chromeclass-toolbar-additional");
button.setAttribute("tooltiptext", "Replace an existing bookmark"); = "url(" + icon + ")";
button.addEventListener("command", main.action, false);

This code is thanks to dgutov and is seen in full context at his repository here at GitHub: dgutov / bmreplace / bootstrap.js.

Watch for a snippet that you can copy and paste into Scratchpad, and then run on Gists@GitHub here: _ff-addon-snippet-AddToolbarButtonToPalette.js . It is based on the code from the repo above.

Here are some discussions at Mozillazine about adding a toolbar button in a Bootstrap addon: Programmatically add a button to toolbar palette?

The advantage to adding the toolbar button to the palette rather than creating an element and then appendChild to the toolbar (document.getElementById('nav-bar')) or appendChild to the addon bar (document.getElementById('addon-bar')) is that once in the toolbar palette, users can configure it through the customize menu. They can drag it to the addon bar or to the toolbar.

Styling the button

Most toolbar buttons have icons. To attach an image to the button we use standard Mozilla skinning facilities. If you're unfamiliar with how that works, read the skinning section of Jonah Bishop's excellent Toolbar Tutorial. Although the article covers creating an entire toolbar, rather than just a button, it has a great explanation of the techniques we'll use here.

Icon size

Toolbar buttons can have two different sizes -- big and small. This means you'll need to provide two icons for each of your toolbar buttons. The dimensions of the icons in various applications for both modes are summarized in the following table (feel free to add information about other applications):

Application (Theme name) Big icon size Small icon size
Firefox 1.0 (Winstripe) 24x24 16x16
Thunderbird 1.0 (Qute) 24x24 16x16

The stylesheet

To set the image for your toolbar button, use the following CSS rules:

/* skin/toolbar-button.css */
#myextension-button {
    list-style-image: url("chrome://myextension/skin/btn_large.png");
} toolbar[iconsize="small"]

#myextension-button {
    list-style-image: url("chrome://myextension/skin/btn_small.png");

Applying the stylesheet

Remember to attach the stylesheet you created to both the overlay file and the Customize Toolbar window. To attach it to the overlay, put this processing instruction (PI) at the top of the overlay file:

<?xml-stylesheet href="chrome://myextension/skin/toolbar-button.css" type="text/css"?>
Note: The CSS file with your toolbar styles needs to be included in the overlay file, as you would expect, but also in the chrome.manifest file. This is very important because the toolbar customization dialog won't work correctly without this.

To include the style on your chrome.manifest file:

style chrome://global/content/customizeToolbar.xul chrome://myextension/skin/toolbar-button.css

If you are developing for Firefox 1.0, attach it to the Customize Toolbar window (chrome://global/content/customizeToolbar.xul) using skin/contents.rdf. The code looks like this:

<?xml version="1.0"?>
<RDF xmlns="" xmlns:chrome="">
<Seq about="urn:mozilla:skin:root">
<li resource="urn:mozilla:skin:classic/1.0"/>
</Seq> <Description about="urn:mozilla:skin:classic/1.0">
<chrome:packages> <Seq about="urn:mozilla:skin:classic/1.0:packages">
<li resource="urn:mozilla:skin:classic/1.0:myextension"/> </Seq> </chrome:packages> </Description> <Seq about="urn:mozilla:stylesheets"> <li resource="chrome://global/content/customizeToolbar.xul"/> </Seq> <Seq about="chrome://global/content/customizeToolbar.xul"> <li>chrome://myextension/skin/toolbar-button.css</li> </Seq> </RDF> 

The skin/contents.rdf file is denigrated in developing for later releases of Firefox. Extensions for Firefox/Thunderbird 1.5 and above should instead use something like this in their chrome.manifest:

skin	myextension	classic/1.0	chrome/skin/
style	chrome://global/content/customizeToolbar.xul	chrome://myextension/skin/toolbar-button.css ia

Take note of the Packaging section in this article; you may need to include .jar references if you are delivering your extension as an .xpi file.

Common mistakes

This is a list of the most common mistakes made by extension authors, including both symptoms and solutions.

Problem: The whole set of default buttons is painted on the toolbar or in the Customize Toolbars window, instead of your own icon.

Caused by: Malformed or not applied stylesheet.

Solution: Check to be sure your stylesheet is correct, make sure your contents.rdf (or chrome.manifest) is correct, and be sure you didn't forget to apply the stylesheet to customizeToolbar.xul.

A list of commonly overlayed windows with toolbars

URL Application and affected window(s) Palette id
chrome://browser/content/browser.xul Firefox - Main window BrowserToolbarPalette
chrome://navigator/content/navigator.xul SeaMonkey 2.0 - Browser window BrowserToolbarPalette
chrome://messenger/content/messenger.xul Thunderbird - Main window MailToolbarPalette
chrome://messenger/content/messenger...gercompose.xul Thunderbird - Compose window MsgComposeToolbarPalette
chrome://messenger/content/addressbo...ddressbook.xul Thunderbird - Address book AddressBookToolbarPalette
chrome://editor/content/editor.xul Kompozer - Main window NvuToolbarPalette
chrome://calendar/content/calendar.xul Sunbird - Main window calendarToolbarPalette

More information