There's a Thunderbird on the Thunderbird features page: The third paragraph under "Tabbed Email" reads: "Tabbed email lets you keep multiple emails open for easy reference. Doubl-clicking or hitting Enter on a mail message will open that message in a new tab." "Doubl-clicking" should be "Double-clicking".
The irony of a typo in a bug report about a typo. "There's a *typo* on the Thunderbird features page."
Fixed in r132196/r132197