Guess you should not trust everything you read and from a tech site no less - go figureBeg to differ, Lord.
That article is out-of-date (Kali changes), and the author is wrong, anyway.
For a number of years, default browser for Kali has been Firefox, but the ESR version. Not IceWeasel.
Current version is
@aaryan if you are going to use Kali, stick with what is supplied, Kali updates regularly.
Having Firefox 84 will not serve you any better than having FF-ESR78.
And note what I said at
You are seriously wasting our time and resources by not trying a Distro like Ubuntu or Mint or Manjaro to learn about Linux before trying Kali.
I mean this to help you.