If you open the revision history for a file you get a new window that has a toolbar on top. The toolbar has 3 buttons on it: Refresh, back and forward. If you right click on this toolbar you get a context menu with a single item but no text. The item is a checkbox that is enabled by default. If you click on the context menu item, the toolbar is hidden. However, since the context menu is only shown when you right click on the toolbar, there is no way to bring the toolbar back!
I think that the context menu should be removed altogether, so that it is no longer possible to disable the toolbar.