Control-t transpose characters от Logical Extreme Technology

Many terminal applications including emacs, and from this lineage, most MacOS inputs, support control-t to transpose the characters around the cursor. Firefox currently lacks this feature, though they would be willing to support it: https://bugzilla.mozilla.org/show_bug.cgi?id=433972

In the meantime, this add-on adds the control-t shortcut to inputs and contenteditable elements.