This question already has an answer here:

Even with dev null and disown..
web browser is still reporting errors to the terminal
it launched from of.

  web_browser < /dev/null > /dev/null 1>&2 & disown

marked as duplicate by Gilles shell Feb 12 '17 at 21:11

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You've got your redirections in disorder.

web_browser </dev/null 2>/dev/null 1>&2 & disown

What you did was first to redirect standard output to /dev/null, and then again to standard error.