the notebook-5.7.4 (and 3) do launch Firefox when my default Browser is Chrome

[stonebig]

Is there a correlation between this odd behavior and Notebook-5.7.3_or_4 ?

should I clean some setting parameters ?

[stonebig]

other remark, but maybe it appeared before, the widget below indicates a time of music of 75 minutes when it is 7 seconds.

[takluyver]

Possibly similar to #4304; it may be that Firefox is set as your default application for HTML files, even if it's not your default browser.

The audio widget is rendered by the browser, so it's presumably a browser bug. I've seen it too; it's possibly specific to using data URLs, or to the particular wav format (e.g. bitrate) we're using.