The Firefox PDF Viewer has a sidebar which displays pages, the document outline, attachments, and layers.
I believe that the viewer would be much improved if these different modes for the side bar retained separate buttons (as they once did) instead being forced into a drop down which takes an additional click to use.
Should it be unclear what the buttons do, they ought to have a small text label when you hover over them that names each.
I also think that "document outline" should be the default or there should be a way to set one setting or another to the default while using the PDF viewer.
Also a "expand all" and "collapse all" button on the document outline would be useful for PDFs with many nested sections.
