Sizzy Does Not Simulate Browser Engines
Sizzy only simulates viewport size and user agent—it doesn't simulate different browser engines.
For example, setting the user agent to Firefox while Creating Custom Devices or Cloning Devices—Create Modified Versions of Existing Devices still renders the page using the Chromium engine, instead of Firefox's Gecko.
Therefore, there might be minor differences between how the website looks in Sizzy vs how it looks in a "real" Firefox browser.
Updated 03 Mar 2023
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