Created attachment 435984 [details] [diff] [review]
Just noticed that we have one id in messageHeader.css that doesn't seem to exist in the tree. We didn't had it in 1.9, 1.8 and 1.7 either. I guess the attachment list was a tree in earlier versions?
The tree was added in bug 75691. Trees then got converted to <outliner> or <listbox> by bug 110155 (well the patch ended up on bug 110156). Unfortunately nobody noticed that the CSS needed to be updated...
Comment on attachment 435984 [details] [diff] [review]
But then again I don't think these style rules make much sense anyway.