First tried to install their new addition, but after ten created versions and error from Firefox that the add-on damaged, tried to put another addition that is well established. Then I package.json only added +1 to the version and added as a new version, of mistakes, of course, was not, but when you try to install new version got the same error – the addon is corrupted.
What’s the problem?
I downloaded the file for the latest version of your add-on and it worked when I tried installing it. Trying to install it directly from the developer page won’t work, though, since unlisted add-on files are hosted in a different domain.
As for your second observation, changing a published add-on file will break its signature, which will trigger an error in Firefox by default.