feat(browse): add Firefox support via BROWSE_BROWSER=firefox

[HMAKT99]

Summary

• BROWSE_BROWSER=firefox launches Firefox instead of Chromium
• Introduces getBrowserType() resolver — replaces 2 hardcoded chromium.launch() calls
• Both launch() and handoff() use the resolver
• When unset: zero behavior change

BROWSE_BROWSER=firefox browse server

Note: PRs #372 (WebKit) and #373 (Edge) build on this refactor. Merge this first.

1 file, 10 lines changed

browse/src/browser-manager.ts

Test plan

• All 548 existing tests pass
• Default: chromium unchanged
• No remaining hardcoded chromium.launch()

[garrytan]

Thanks for this! Closing — Firefox support isn't something we've had user demand for. gstack is built on Chromium via Playwright and that covers our use cases well. If this becomes a real need from users down the road we'll revisit, but for now we're keeping the browser scope tight. Appreciate the work!