Apologies for resurrecting an old thread, but it’s to save starting a new one.
I’ve made a Chrome/Firefox extension which adds the functionality described above. It’s already available in the Chrome webstore, and it’s been submitted to Mozilla Add-ons for review, so should be available for Firefox soon.
Any suggestions for improvement or bug reports are appreciated, and you can view the source on Github.
Edit: After a brief 6 week wait in the review queue, the Firefox version has been approved