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This page pairs the support claims that otherwise live on separate pages: which browsers run on which operating systems, what “reload” means per framework, and which CSS tools need dependencies installed. Each table links to the page that covers setup in depth.

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Browsers × operating systems

All Chromium-based and Gecko-based targets work on Windows, macOS, and Linux. Safari is the exception: it is an alpha target that requires macOS with full Xcode. See Browsers available for target names and flags, and Building Safari extensions for the Safari workflow and limitations.

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Frameworks × dev update model

Every framework gets automatic detection, bundling, and dev-time updates. What differs is the update model: whether an edit hot-swaps code in place or reloads the surface. See Reload and HMR for the underlying tiers.

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CSS tooling × what installs automatically

Plain CSS and CSS Modules are built in. Preprocessors resolve their toolchain on first detection: Extension.js installs the missing packages and asks for a restart. Tailwind rides through the PostCSS pipeline and is installed by you.

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Package managers

npm, pnpm, yarn, bun, and deno are all supported for create, dev, and build. Deno projects scaffold a deno.jsonc instead of a package.json; the toolchain is manifest-agnostic. See Create your first extension for the Deno-specific notes.