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CloseDeveloper reply by Michael J Gruber
Rated 4 out of 5 stars
This project appears to have been dead for some time now. The mailing list no longer exists, and the archives stopped abruptly in Jan 2012 (http://www.mozdev.org/pipermail/quotecollapse).
It works great, as far as it goes, and it can even be extended to include a very-helpful keybinding to toggle behavior by hacking via keyconfig as suggested here: http://quotecollapse.mozdev.org/customising.html. But the Style hacks are no longer applicable with current versions of Thunderbird, and since the community is dead I suppose we can't expect any updates such as properly integrated keybindings or customizations. What it is is what you get (unless somebody picks up the source and carries this on to completion).
It's annoying that it collapses all quotes completely - it should be tunable for context. But it's better than nothing particularly in long discussions with people who use inline comments or bottom posting without trimming any content.
Please try version 1.0 and check out the Customization section of the website.
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