Add a textarea to the test page elements to be found list.
Fix the handleKeyboardEvent method so that it's not half-assed and does what it should.
Fix an incorrect CSS selector that did not filter out input elements with type=hidden.
Do not capture the keyboard event if a content editable element or text-like input is focused.
Include elements with contenteditable=true as targets.
Load the hint styles in contentscript CSS file through the manifest.