User selector appears over non-Chrome browser warning

[ES-Alexander]

Bug description

Steps to reproduce

1. Open a non-Chrome browser
2. Open Cockpit (the Extension version)
3. The user selector appears, on top of the browser warning

Primary pain point(s)

You can end up doing partial configuration before needing to scrap it and do it again in a different browser.

Additional context

No response

Prerequisites

• [x] I have checked to make sure that a similar request has not already been filed or fixed.