I have confirmed that my test adapters do not run on Chrome and Safari. I was debugging, and breakpoints inside adapters just don't get into Chrome / Safari when they work fine in Firefox / IE. So for Chrome / Safari, IIS just ignores the display.
The file My AdapterMappings.browser is as follows:
<browsers>
<browser refID="Default">
<controlAdapters>
[...adapters here....]
</controlAdapters>
</browser>
</browsers>
This should provide a match for all browsers, right?
I used Charles proxy to check which senders were sent. It:
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/532.5 (KHTML, like Gecko) Chrome/4.1.249.1064 Safari/532.5
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/531.22.7 (KHTML, like Gecko) Version/4.0.5 Safari/531.22.7
Any idea why this would be? Does everything I read tell me that my browser mappings are correct? And as I said, this works for IE / Firefox, so I know that my configuration is technically correct.