Hey Product Hunt 👋 I am launching Mobile Simulator (MSIM): a free Chrome and Firefox extension for multi-device responsive testing. The pain: DevTools is great for one viewport. Real QA is comparing phones and tablets together, catching layout bugs, and showing clients something that looks like a real device, not a resized window. What you get: • Open multiple devices side by side • Sync scrolling across previews • One-click rotate • Large device library with current flagships (iPhone 17 / 17 Pro / Air, Galaxy S25, Pixel 9, modern iPads) • Custom width/height when you need a weird breakpoint • Free core, no account required Fresh in this version: 1) Updated device library for newest phones/tablets 2) Firefox desktop build live on AMO 3) Brand site at https://msim.app with direct install links Install: • Site: https://msim.app • Chrome: https://chromewebstore.google.co... • Firefox: https://addons.mozilla.org/en-US... What it is not: a real-device cloud lab (BrowserStack-class). It is a fast in-browser multi-device preview for frontend and design QA. I would love feedback from people who do responsive work daily: • Which devices should be in the default “Popular” set? • Any sync/scroll edge cases on your stack? • Firefox workflow gaps vs Chrome? Thanks for trying it. I will be here all day answering comments.

Mobile Simulator MSIM

Side-by-side mobile testing in Chrome & Firefox

Side-by-side mobile testing in Chrome & Firefox