Rated 5 out of 5 stars

Finally managed to understand how to use it, together with related Thunderbird limitations.

The documentation should clearly state two things:

1) the toolbar button is grayed if you set mailnews.wraplength to zero. (Unfortunately there is no tooltip on a grayed button that suggests a possible fix. On the other hand, keeping the button enabled and bugging the user with an error message might seem too intrusive.)

2) "STRG" in description is the same as "CTRL" on English keyboards.

This review is for a previous version of the add-on (1.3). 

Thanks for the feedback. I updated the description.