Creating toolbar buttons

From MDC

This article explains how to add a toolbar button to a Toolkit application (such as Firefox, Thunderbird, or Nvu) 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.

[edit] 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.

[edit] 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;"
    oncommand="MyExtension.onToolbarButtonCommand(event);"/>
</toolbarpalette>

Notes:

• The id of the palette (BrowserToolbarPalette in the example) depends on the window whose toolbar you wish to insert a button into. 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.
• Put the command to be executed when the button is clicked in the oncommand attribute. If you need to handle middle-click, add an onclick handler and check event.button in it.

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>.

[edit] Styling the button

Most toolbar buttons have an icon. 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.

[edit] 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):

[edit] 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");
}

[edit] 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"?>

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="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
     xmlns:chrome="http://www.mozilla.org/rdf/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

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

[edit] 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.

[edit] A list of commonly overlayed windows with toolbars

[edit] More information

• XulPlanet.com references: <toolbarbutton>, <toolbaritem>.
• How to adjust toolbarbutton's label position
• A forum thread about adding an item to the toolbar (instead of just adding it to palette) right after an extension is installed. Note that doing this is not recommended.
• There is another page on mdc with information about adding buttons to various windows in SeaMonkey. Includes useful information about overlays for ChatZilla.