Seen in Firefox on beta labs as of Nov 25 (Chrome behaves correctly):
Login and navigate to some page with text, e.g. as Selenium_user/User:Selenium_user
Without touching anything on the page, click the "Link" icon in the menu bar.
Expected: First word in the page is highlighted and link UI appears, referring to highlighted text.
Actual: Link icon shows being pressed, but no link UI appears.