Rated 5 out of 5 stars

0e8h, pizzaninja, mr_no_one.
Version 0.6 didn't erase passwords, it stores it in new format and new folder. You can back to 0.4 version and all of your passwords will be back!
And you can use Password Exporter extension ( https://addons.mozilla.org/en-US/firefox/addon/2848 ) to backup passwords and move it from 0.4 to 0.6 version, from firefox db to kwallet and back.

This review is for a previous version of the add-on (0.6).  This user has other reviews of this add-on.