I've been having some problems with some browsers downloading my .air apps as .zip files, even replacing the file extension. I figured it was a Mime type problem, and sure-enough...
This is from the AIR release notes:
Setting the mime type in your Web Server for AIR applications
In order for client browsers to recognize an AIR application when being downloaded, the Web Server hosting the AIR applications needs to map the following MIME Content Type “application/vnd.adobe.air-application-installer-package+zip” to the Apollo extension “.air”. For example, for an Apache Web Server you will add to the AddType section: AddType application/vnd.adobe.air-application-installer-package+zip .air
So for Apache, just add this to your config:
AddType application/vnd.adobe.air-application-installer-package+zip .air
I had some weird problems with the badge-installer not working on a couple OSX machines, I wonder if this will fix it.