Load any url and the status bar will show 'Cancelled opening the page'. The activity viewier will also show many items as cancelled, but the page loads complete and without error. WebKit r17425
I'm seeing this too with r17515. The Activity window is also showing a variety of items as cancelled even though the page has loaded fine.
Created attachment 11335 [details] Activity window
Created attachment 11383 [details] patch to fix the problem; no layout test, though
Comment on attachment 11383 [details] patch to fix the problem; no layout test, though r=me
Committed revision 17598.