I use Firefox mobile day to day and keep both Mull and Brave installed. Unfortunately right now Brave is recommended on mobile for privacy:

Firefox (Gecko)-based browsers on Android lack site isolation,1 a powerful security feature that protects against a malicious site performing a Spectre-like attack to gain access to the memory of another website you have open.2 Chromium-based browsers like Brave will provide more robust protection against malicious websites.

https://www.privacyguides.org/en/mobile-browsers/#brave-sync

Hope to switch back to Firefox & Mull only once that’s fixed