Preview Web pages Across Multiple Browsers and OS

BrowserLab lets you preview web pages across multiple browsers and operating systems. Accurately pinpoint compatibility issues and compare web pages at a glance to easily identify differences and potential problems. Preview full screenshots with multiple view options and customizable test settings.

You can get a full-view screenshot, even beneath the fold, or compare how your web page looks in two browsers, side by side. With the Onion Skin View, spot discrepancies at a glance by overlaying two screenshots on top of each other. You can focus on specific areas with custom positioning of the screenshots and adjust the opacity from 0–100%.

Source: https://browserlab.adobe.com/en-us/index.html#state=browse