Nightly builds of Firefox for Windows now come in three flavours – the standard zip file, the installer build and now a build that can install using Windows Installer (MSI). From what I can gather, this has been done to aid deployment of Firefox across Windows-based enterprises.
Thankfully, Mozilla seem to be going down the route of offering the MSI build in addition to the standard installer, instead of replacing it altogether. I’m not a big fan of MSI – it’s very slow, especially when uninstalling, and doesn’t offer the best compression ratios – the MSI build is 5.4MB as opposed to the standard installer’s 4.6MB (although the zip build is bigger at 6.3MB). The standard installer on the other hand is quite fast in comparison. OpenOffice.org appear to have taken the other route and with their preview of version 2.0 have only provided an MSI build, even though I didn’t see anything much wrong with the installer they’re currently using for 1.1.4.
The MSI file looks like it has been made with the freeware MakeMSI tool, instead of WiX which was Microsoft’s famous first entrance into the open source arena (more details here). Make of that what you will.