Before I got this screenshot of the measure tool showing what the how to needed it to show, in reality I had this situation:
And more, while reproducing this problem for this page, my transparency area was 798 pixels wide instead. I have no idea what caused this, especially since I am fairly certain that I used the Canvas resize gui properly, like I asked it to make an image area that was 800 pixels wide.
Fixing the problem: a repair of this problem would have been to determine what went wrong. Determining what went wrong would probably involved investigating Fuzzy Selection Tool Options (perhaps it is the anti-aliasing on that, although this should not have mattered with a rectangular selection and I thought about that as I was doing this) and change that or if that failed to file a bug report and otherwise make sure that the application works as expected. Fixing it was more fun and ultimately less work though.
All of my Droste Effected Desktop images should have this problem recursively embedded in them. I kind of like it that way.
These well-behaved little girls are almost honest screenshots. I am very proud of them.
I opted to clone away the Bookmarks Toolbar instead of once again, making the browser window to be the correct dimensions.