Use Firefox Developer Edition on MacOS

[Eliot Hertenstein]

Describe the bug
jupynium always launches jupyter in Firefox.app, even though the default browser is set to Firefox Developer Edition.app.

Output of jupynium --version

Jupynium v0.2.2.dev10+gc6fdf2f

Output of nvim --version

NVIM v0.9.4
Build type: Release
LuaJIT 2.1.1700008891

   system vimrc file: "$VIM/sysinit.vim"
  fall-back for $VIM: "/opt/homebrew/Cellar/neovim/0.9.4/share/nvim"

Run :checkhealth for more info