An extension installed globally for all users (in /usr/share/mozilla/extensions) does not load for an unobvious reason

 {
   "manifest_version": 2,
   "name": "Extension Name",
   "version": "0.1.2",
   "applications": {
     "gecko": {
       "id": "{0a1b2c3d-0123-abcd-cdef-a0b1c2d3e4f5}"
     }
   }
 }

The solution is found. There were two problems at once. First, in order for the extension to be loaded by the browser, manifest.json (which is in the root of the directory with the extension) must have the following required minimum: { "manifest_version": 2, "name": "Extension Name", "version": "0.1.2", "applications": { "gecko": { "id": "{0a1b2c3d-0123-abcd-cdef-a0b1c2d3e4f5}" } } } And the name of the .xpi file of the extension (which is actually a zip archive) or the directory with the unzipped extension must match the "id" value in manifest.json. Secondly, it is necessary to check the permissions of the files and directories. In my case, the permissions of the extension directory, for some strange reason, were 700. At the same time, the extension did not have an "id" key in manifest.json, which additionally hindered diagnosis of the problem. The illogical thing here is that when you install the extension in the user's profile, Firefox installs it without any problem, regardless of the invalid mainfest.json. There's no reason for this difference in behavior, it's just a headache for system administrators.