I found the related topic: https://support.mozilla.org/en-US/forums/contributors/711723

I trully understand that it is the known issue and it has no any solutions today?

That "related topic" was a discussion among the support contributors and administrator about having a unified or standard response in this forum about the signing feature.

What "issue"? It's a new feature intended to "protect" users from extensions that might do malicious, unwanted changes to Firefox user preferences. Starting with Firefox 43 all extensions need to be signed by Mozilla. I have seen nothing about self-signed extensions being allowed. IMO, it would defeat Mozilla having control over the situation that brought about the signing feature.

As far as differences on different PC's, maybe they aren't all running the same version of Firefox or maybe the primary user has already "flipped the switch" to disable that new feature? xpinstall.signatures.required

The real "fix" is to submit that extension to Mozilla Add-ons for signing, and if you want it to be signed and returned to you as a "private" extension, make sure you select that option.

The add-on was signed by Mozilla Add-ons with using the official documentation, but was not published as private. Is it true.

Problem is the signed add-on does not work in Firefox 43 at part of users, when it updated by web.

Added: in that "related topic" someone Madasan says about "known issue": https://support.mozilla.org/en-US/forums/contributors/711723#post-67686

You can try to sign the extension another time.

Try to ask advice at the Add-ons forum site.

• https://discourse.mozilla-community.org/c/add-ons