[Redmi note4 -Miui 10 Global 8.12].

For testing self written Html/Javascript scripts in different mobile browers .I am trying to change the default browser .I could change it the first time in App setting-- Default browser (Mi browser to Chrome) ,but now on changing  Chrome to Firefox ,the default browser is not changing .The Html/Js  files keep opening up in Chrome and  also the Javascript is not recognised (even after enabling Javascript in Chrome settings).

I have cleared the cache memory and rebooted( for the browser change to update),however the issue still persists.

Please let me know how to change the browser and also if there are any more settings to get Javascript recognised.