The add-on downloaded from this site could not be installed because it appears to be corrupt.

[JWNOR]

I am trying to install the legacy extension "norwellht".
I followed the instructions in the "README.md" file at "https://github.com/xiaoxiaoflood/firefox-scripts/tree/master/extensions".
I managed to install "userChromeJS" for both scripts and extensions by following the instrustions in the file at "README.md" file at "https://github.com/xiaoxiaoflood/firefox-scripts".
However, when I drag and drop the "norwellht.xpi" file from "https://github.com/xiaoxiaoflood/firefox-scripts/tree/master/extensions/norwellht" onto the "Add-ons Manager" tab, I get the following error:
"about:addons
The add-on downloaded from this site could not be installed because it appears to be corrupt.
OK"
I then looked in the "Issues" on "https://github.com/xiaoxiaoflood/firefox-scripts/issues" and found the issue #343, "Here are the updated chrome/utils files for 136+" at "#343".
Using the files provided there I then updated files that go into the chrome and utils folders as well as I updated the "config.js" file.
However, I still get the error message and cannot install "norwellht" or any of the other legacy extensions that I tried from "https://github.com/xiaoxiaoflood/firefox-scripts/tree/master/extensions"
I am using Firefox version 137.0.1, build ID 20250407111027.
My "User Agent" is "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:137.0) Gecko/20100101 Firefox/137.0" and my OS is "Windows_NT 10.0 19045".
Is anyone else having similar problems?
If so, what is the solution?
I have tried to read through the issues and discussions but they are a little too technical for my understanding as to whether they are related to this issue or not... It seems that with each FF release new issues come up that may appear similar but may have different causes and/or solutions... So it is difficult for me to determine what to try...
Thanks :)