Right-click a link to copy its text; also optionally offers ability to right-click drop-down menu items, buttons, and other form controls to get their text or values
A suite of tools for developers.
Firefox browser add-on to open an HTMLEditor editor in a new tab.
Right click an image (including a background image), SVG element, or canvas containing a QR code to decode.
Display the results of an XSLT 1.0 transformation (including on a currently loaded page), on a one-shot or Grease-monkey-like per-site basis
Simple context menu add-on to append to, rather than replace, current contents of the clipboard. Also with a "clear clipboard" item.
Jump to the nearest anchor above a selection
Right-click a Mediawiki-style link (as used at Wikipedia) to be able to go directly to its edit page.