Playing music and loading backgrounds from your local device relies on the File System Access API, which full specification is currently implemented only on Chromium-based browsers.
This feature should work by default on Chrome, Opera and Edge; on Brave, you'll need to enable it in chrome://flags/#file-system-access-api.
On Firefox, Fill Opacity may not work properly with Radial analyzer, due to this bug.
Visualization of live streams currently DO NOT work on Safari, as documented in this bug report.