XULRunner Support

By Stephen Kellett
3 April, 2007

About a month ago we hadn’t heard of XULRunner. Then the folks at Songbird emailed us asking if our JavaScript tools supported XULRunner.

Its easy to miss a new tool or technology what with all the various development directions people are taking. XULRunner is a platform independent way to write applications using the same technology used to create Firefox and Thunderbird. You use the XPCOM, XUL and JavaScript technologies to create your application. With a bit of magic it then runs on your platform of choice. Songbird are using XULRunner to create a platform independent media player. I guess they know their target market, they are founded by the same people that did Winamp and Yahoo! Music Engine.

Given that we already supported JavaScript for Firefox and Flock support for XULRunner seemed like a natural fit. Ideally it would have worked out of the box, just change a few settings on the UI of our tools and off you go. It didn’t turn out that way, although now we’ve made the appropriate changes, its as trivial as selecting xulrunner.exe instead of firefox.exe when you are choosing the JavaScript runtime.

The first problem we had was that xulrunner.exe doesn’t use the js3250.dll DLL directly, it does it via the xul.dll DLL. As a result the UI and the stub couldn’t find the js3250.dll and thus couldn’t determine the version information we use to choose how to interact with js3250.dll. So we needed to support that.

The second issue was that each js3250.dll we’ve encountered has some internal differences that make line numbers inconsistent unless you use a build against the same header files used for that build. Very annoying, but thats how it is. So we need to know if its Firefox 1.0, 1.5, 2.0, Flock 0.7, or xulrunner to choose the appropriate way to interact with the target. If our tools don’t know they assume you are using the latest and greatest and give you the firefox 2.0 treatment. XULRunner needs the 1.5 treatment not the 2.0 treatment so we had to put in a check for that. Also, the version ids on xulrunner.exe shipped with Songbird are “Personal” and not a version number. Excuse me? Whats up with that? Not very useful information. It should read “1.8” or something similar given that XULRunner is currently at Hopefully someone will fix that.

A third issue was a killer. Songbird triggers a hook that causes a fatal crash. Whoops, how did that get past testing? Same way any other bug does I guess 🙁 Thats life, we are not perfect, so chalk that one up to experience.

We also needed a few XULRunner specific tweaks. For example when you are launching a XULRunner application you are looking for .ini files not .html/.js files.

To sum up, all our JavaScript tools now support XULRunner. This should help all of you using XULRunner to create platform neutral apps using Mozilla technology. If you have any specific issues please let support know at the usual address.

Fully functional, free for 30 days