A Firefox that feels
like yours.

Try, build, and maintain Firefox themes.
Pick a starting point. You’ll be working in a few commands.

Python 3.9+ Firefox installed macOS, Windows or Linux

Install fxcss

Choose one method. Both include the image tools; then continue to step 02.

Installs pipx if needed and confirms the plan for your chosen path.

curl -fsSL https://fxcss.com/install.sh | bash -s -- --intent maintain

Use pipx directly on macOS, Linux, or Windows.

pipx install "fxcss[images]"

Run from your theme repository to add PR previews, Firefox checks, and release images.

fxcss init --watch --showcase

Review the generated workflows.

Commit them to your theme repository to begin running checks on GitHub.