First WebExtension working local, signed OK but cannot install



I just have finished my first extension. If I install it temporary for debugging purposes it works. After uploading to AMO (only for private use) and a few adjustments it was signed without any problems. Then I downloaded my extension and tried to install it in Firefox. But I always get the error message: “This addon could not be installed because it seems to be damaged” I dont’t know the exact wording, in German it is: “Dieses Add-on konnte nicht installiert werden, da es beschädigt zu sein scheint.”

I don’t understand why it is not working. Any help appreciated.

If more information is needed please ask me.

Thanks a lot in advance.

Kind regards,


It’s done :smile:

I had written by name in manifest.json with an Umlaut (ö). After changing to “oe” it is running.

(Martin Giger) #3

Special characters should not be an issue if the file is saved as UTF-8.


I have the same problem: if I have German special characters in _locales/de/message.json I cannot load the temporary extension (I get an error “There was an error during installation: Extension is invalid”). When I remove those characters everything works file. what do you mean by saving it as UTF-8? Is there a way to make it work when I load a temporary extension for development?

(Martin Giger) #5

There are multiple ways to represent characters in bits. These are the different character encodings a file can have. In web things that’s sometimes called “charset”. And one of those ways is called “UTF-8”. And for your extension to work properly you need to save the files using that encoding. How exactly you achieve that depends on your editor/IDE.


Thank you so much… this was exactly the problem. Everything works fine now!