What are the symptoms of this issue? Are there any error messages?

Same situation. Fresh install of latest Tumbleweed (20251007) that provides FF 143.0.3. Attempting to install an extension hangs upon clicking the "Add to Firefox" button. No error messages. The addon's tab just goes catatonic (but it's closable.). In the past, when this occurred on my laptop I let it sit overnight to see if it would eventually complete or at least issue an error message. Instead FF just crashed. Please don't make me use Chromium.

User account permissions problem?