Security Level selector does not get confirmation before restarting

Since browser restarts are destructive actions that result in the loss of open windows and tabs, they're typically accompanied by confirmation dialogs in both Firefox and Tor Browser – for example:

I believe this feature is currently missing from our new Security Level selector, which requires a restart in order to apply new any changes.

At least one forum user has expressed surprise that they lost all their tabs in the process of selecting a new security level. I imagine the problem is more widespread, and may contribute to the frustration with the new user flow (although #43922 (closed) is a greater pain point).

We do warn that "This will close all windows and tabs" in the Change security level dialog, and the primary button now reads Save and restart – however it's likely that many users do not notice this text and are being guided by muscle memory instead. In any case, a confirmation dialog would be best practice for a destructive action like this.