"TwemojiMozilla.ttf being used by another process" error when launching Roblox

This happens because of three circumstances:

1. You've opted to use a different emoji type under Bloxstrap's mod presets
2. Roblox is trying to upgrade
3. Roblox is running in the background

If you're launching Roblox from different accounts, see this related page, as this will prevent Roblox from unnecessarily updating: https://github.com/pizzaboxer/bloxstrap/wiki/Launching-from-different-accounts-always-forces-a-Roblox-upgrade

Otherwise, you may be getting this after an actual Roblox update. In which case, Roblox is still running in the background, so ensure that it isn't first, such as through Task Manager.