The solution for this was to create a default location for the icon, so that it could be extracted without having to install the add-on and resolve the chrome URL. This is a chrome URL, so it has the disadvantage that it doesn’t work when the add-on is disabled, or when the install dialog for the add-on is displayed. Traditionally, this icon was defined using the iconURL tag in the install.rdf manifest. On Firefox 3.6 and earlier versions, the Add-ons Manager displays a 32 x 32 px icon for every installed add-on. All art is based on this simple SVN icon from the Wikimedia Commons repository. You can download the add-on from this link. I created a simple demo add-on that showcases icons that work in Firefox 4 for the 3 major platforms: Windows, Mac and Linux. Those who seek to create professional-looking add-ons will most likely have to pay a professional graphics designer to work on them, and for this they need a clear specification of the icon styles and dimensions that are necessary for each platform. He’s right toolbar buttons and icons in general can be a complicated issue for many developers.

Nils Maier, a fellow developer, has pointed out that the changes in toolbar buttons deserve a more in-depth look than the couple of paragraphs I dedicated in my previous post. We have been discussing Firefox 4 add-on compatibility for quite a while, and there are a couple of pain points that are important to revisit. I will create a new post and link it from here if and when this bug is solved.

Update: the resolution of bug 616472 (see comments below) may have a significant impact on this documentation. They’re much simpler, so I strongly recommend you use them instead of the ones detailed here, even though they still work. Update 2: there’s a new blog post up that details the new theme rules.

Mozilla firefox addons missed icons