Some of the feedback we received from Fennec Alpha 1 (and we have received a lot, thank you!) has been about the download and “on disk” size. Fennec is based on XULRunner, Mozilla’s runtime platform. Therefore, when you install Fennec, you’re installing the XULRunner dependency too. Fennec is ~ 1MB in footprint size, while XULRunner is ~ 25MB.

Yes, Fennec’s overall size is a bit big for a mobile browser. But it is a full blown browser, with all the web support of a desktop browser. It also supports the same add-on system as desktop Mozilla applications, like Firefox, Thunderbird and Songbird.

There’s another benefit of having XULRunner installed on the device: Any other XUL-based application can use the XULRunner runtime, without needing to install anything extra. Applications like Chatzilla, XULMine, XULExplorer and Prism could be installed and launched using the shared XULRunner. Keep in mind, Fennec thinks it “owns” that XULRunner and will update it when it needs too.

So, if you installed Fennec A1 and want to create your own XUL-based apps on a mobile device, you have an up-to-date runtime to build on. Here’s a simple way to get started with XULRunner (on mobile too).