Firefox's performance settings

Firefox automatically uses settings that work best with your computer. You can modify these settings in your Firefox Settings page. In the Menu bar at the top of the screen, click Firefox and then select Preferences or Settings, depending on your macOS version.Click the menu button and select Settings. In the General panel, go down to the Performance section and uncheck the box next to Use recommended performance settings. You will then be able to change the following setting:

Use hardware acceleration when available: This setting allows Firefox to use your computer's graphics processor, if possible, instead of the main processor, to display graphics-heavy web content such as videos or games. This frees up resources on your computer so it can run other applications, like Firefox, faster. This box is checked by default but the feature isn't available for all graphics processors. You must restart Firefox after changing this setting, before it will take effect.