I’ve been looking at how to get a more familiar set-up on Windows, something more similar to what I have on Linux or macOS.

The default bash terminal that comes with mozilla-build is not great for me (I’m used to zsh). Also, mozilla-build comes without a package manager, which means that software I need for managing e.g., my dotfiles doesn’t work.

It’s documented that you can invoke mach outside mozilla-build, and that page does have a bunch of interesting tips, but nothing too concrete.

So while I tried to get that working, I decide to write out what I did in order to hopefully make it easier for someone else.

Installing MSYS2 and some basic dependencies.

First we’re going to need some basic software:

Installing our shell and other MSYS2 tweaks

On an MSYS2 terminal I ran pacman -S zsh (or shell of your choice, or avoid doing it if you’re ok with bash).

Then I tweaked /etc/nsswitch.conf, and set db_home: windows. This allows the windows home directory to be the shell’s home directory, which is easier so that things like ssh / git config don’t need to live in two different places.

Adding a Windows Terminal profile

In the Windows Terminal, we need to create a new profile. Give it the name you want, and the following settings:

Command line

That should be something along the lines of:

C:/msys64/msys2_shell.cmd -defterm -here -no-start -ucrt64 -shell zsh -use-full-path

Some notes:

  • -use-full-path is needed so that things like git or python are visible inside the msys2 terminal.

  • -shell zsh is obviously what triggers the new shell, and you can switch to whatever or omit it to remain with bash.

Start directory

I made that %USERPROFILE% (so, the home directory). You can also set C:\mozilla-unified or wherever you want to have the Firefox checkout.


If you fancy, you can set the icon to something like C:\msys64\msys2.ico or even something like <mozilla-repo>\browser\branding\nightly\default256.png.

Customizing stuff

Now you can customize your terminal and environment much like you’d do on Unix. For me, I imported my ~/.zshrc, ~/.vimrc, etc, and installed nvim (with winget), oh-my-zsh, installed my powerline fonts, etc.

I found some hiccups that I’ll document below:

Python pip path

I use git-revise, moz-phab, mozregression, etc from pip, so I’d like pip-installed commands to be on my PATH. On my Linux/macOS .zshrc I had:

export PATH="$PATH:$(python3 -m site --user-base)/bin"

But that had two issues:

  • The path on Windows is different (it’s user-base/Python{major}{minor}/Scripts).

  • The python3 -m site --user-base command was printing a \r\n, which put an annoying carriage return in the PATH, causing weird stuff to happen with other programs.

In the end what I came up with is:

if command -v python3 > /dev/null; then
  if command -v cygpath > /dev/null; then
    export PATH="$PATH:$(cygpath $(python3 -m site --user-base | tr -d '\r'))/Python$(python3 -c 'import sys; print(f"{sys.version_info.major}{sys.version_info.minor}", end="")')/Scripts"
    export PATH="$PATH:$(python3 -m site --user-base)/bin"

As much an abomination as it is, it works.


There was no msys2 package of neovim (my usual editor on other platforms), but I could install it with winget install Neovim.Neovim.

That works, but turns out on windows nvim looks at a different path for its configuration, so I had to create ~/AppData/Local/nvim/init.vim with:

source ~/.config/nvim/init.vim

For it to pick up my usual config.

On top, running , my usual nvim setup has a number of plugins that didn’t quite work, and various other issues related to stuff not expecting a bash-compatible shell on Windows.

After a bit of painful debugging, I ended up giving up and putting the following in my .vimrc file:

if has('win32') || has('win64')
  set shell=$COMSPEC

Which basically resets the shell to cmd.exe. Stuff just works with that. I also had to create a spell/ directory so that nvim wouldn’t try to download spell files to C:\Program Files\Neovim\... (which didn’t work because of permissions).

Another few tweaks to the ~/.zshrc file were needed, since Git would refuse to use GIT_EDITOR=nvim but GIT_EDITOR=nvim.exe worked.

These are the relevant bits of my zshrc now:

if ! command -v nvim >/dev/null; then
  export VISUAL=vim
  export VISUAL=nvim
  alias vim='nvim'

if command -v cygpath >/dev/null; then
  # This helps with git editor etc.
  export VISUAL="$VISUAL.exe"


Everything else just works. Autocomplete with coc and coc-clangd, etc works perfectly, my usual build setup just works…

Building Firefox

Yay, the fun stuff. The main thing to have into account is that you want this bit in your mozconfig, so that configure picks the right tools / cygwin dlls for the build:

export PATH="/c/mozilla-build/msys2/usr/bin:$PATH"

You shouldn’t need anything else. Maybe we can fix the build system to do this automatically, I filed bug 1801826 for this.

Another thing that threw me off for a bit was that on Linux, I have a setup to allow building with different compilers, and that was overriding AS, which on windows can’t be set to clang-cl.

Since I don’t care about building with different compilers on windows I just avoided setting AS at all.

With all this, I have a comfortable set-up to building and editing code on Windows, similar to other platforms.