Update the version of your browser, I tested with Firefox 115.28.0 ESR and had the corrupt install message then I updated the browser to 140.3.1 ESR and it worked fine. If this isn't an option I'll have to look into what is causing the install file to appear as corrupt for that version.
Edit: It is weird to me that this issue occurred. When I have time I'll try to test it all that changed from 1.28.0 to 1.28.1 was one bug fix nothing major changed so I'm confused as to what caused this to happen.

Edit (2025-10-24):
I’ve identified the issue, but unfortunately it isn’t something I can fix. Starting November 3rd, 2025, developers are required to disclose data collection practices using the 'browser_specific_settings.gecko.data_collection_permissions' key in the extension manifest.

Older versions of Firefox do not support this key. For example, when testing the extension on Firefox 115.29.0 ESR, the following error appeared:

Reading manifest: Error processing browser_specific_settings.gecko: Unexpected property "data_collection_permissions"