Adds: sidebar toggle bar (click on blue vertical separator bar), auto collapsing sticky floating table of contents at top left (hover mouse on it to expand), collapsible sections (click section title to toggle), section links (for getting URL to page sections), auto popup sticky table headers (when table height is longer than the screen), table manipulations (double click empty space of a table cell to show menu).
Greatly improves the user experience! The only bug I noticed is that sometimes scrolling with the mouse wheel or the arrow keys works only in very small increments (i.e., slowly). Could be related to other add-ons to my FF (in particular Yet Another Smooth Scrolling WE), though.
Workaround: page-wise scrolling via PageDown/Up or automatic scrolling via mouse middle-click.