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 build

Use pipx directly on macOS, Linux, or Windows.

pipx install "fxcss[images]"

Create a starter, open its folder, then watch for saved edits.

fxcss new my-theme
cd my-theme
fxcss watch

Save an edit. See the result.

Edit chrome/userChrome.css while watch is running. Firefox reloads the styles.