I think it is a bit weird that the column picker has a fixed layout after the fix for bug 212789 got checked in. I think it would be better if it were put after the last column, and would also scroll when there is a horizontal scrollbar. Also, if there is remaining space in the column header (which is now possible since bug 212789), I think it would look better if it were filled with the column header color. This is what the Outlook Express tree control is doing. I'll attach screenshots.
Created attachment 194871 [details] Mozilla tree view And this is what Mozilla is doing in current trunk build.
That makes the blank space look like an additional column, which it's not. I've seen people try to use that 'extra column' in Windows. Are you sure we want this 'feature'?
Well, I think Mozilla's treecolpicker should resemble windows native treecolpicker, at least under windows.