Mozilla's Firefox web browser uses a platform's native emoji support on the web and in iOS and Android apps. 

On Windows platforms, Firefox uses the 3D Fluent emoji designs instead of their block-color counterparts. Additionally, Twitter's Twemoji designs for flag emojis, which have never been supported by Microsoft's emoji set.

As of early 2022 Firefox on Windows uses Google's minimalist Noto Emoji designs for emojis yet to be supported by Microsoft, such as Emoji 14.0's 🫠 Melting Face and 🫶 Heart Hands.

In 2015 a set of free, open-source emojis was planned by Mozilla for Firefox OS. Abbreviated to fxemoji in the open-source project, this emoji set is not being actively worked on further. This never-implemented set is shown below.