Upon checking for updates, the "Activity" window presents and entry error: "x-webkit-launcher:is-x-webkit-launcher-available.js" (using Mac OS X 10.6.8; Safari 5.1.2)
Could you please provide more detailed steps to reproduce? What exactly should one do to see the problem? When I launch a WebKit nightly to an empty window and immediately open Activity window, there is nothing there. I was testing on Lion though.
Seems this only appears when there IS an update to the Webkit nightlies; when "current" build is installed, there is no error in the "Activity" window. Hope this helps.
The nightly launcher was doing some tricks to make it possible to trigger a Sparkle update from the web page. I suspect that they’re simply not working due to the web content being in a different process now.
This was fixed back in January 2013.