Rated 4 out of 5 stars

Toggle Quotes adds a toolbar button and a shortcut key to QuoteCollapse.
https://addons.mozilla.org/en-US/thunderbird/addon/toggle-quotes/

This review is for a previous version of the add-on (0.9). 

This does not appear to be a review of QuoteCollapse.
I don't mind linking to that add-on-add-on from the description or even integrating functionality.