Why would this be nice? Who would it be nice for? Talkback doesn't affect the way a page is recieved, rendered or any other capabilities of the browser. I can't see any legitimate reason for a page wanting to know this. At best this would seem a waste of developer time that brings up privacy issues. At worst it could be an avenue to security exploits?
I'd think I'd agree. If a user needs to know if talkback is installed and turned on they can run the talkback.exe or talkback executable and check "agent on/off" status. I suspect we could get this hooked up in the "tasks | tools" menu like it is in netscape 4.5x+ browsers.
I have created a bug(internal) to add menuitem for talkback tools.
So let's be honest and WONTFIX this. Another bug covers the user being able to query his own setup; letting websites know can only be useful if they're *wanting* to crash you.
I'm verifying this since a othre bug already exist on bugscape to add menuitem for talkback tools