adding extensions would alter the fingerprint - removing the ability to blend in with the herd which is the whole goal of mullvad browser.
Sounds like librewolf is for you!
you should swap Shazam for the open source “Audile” :
Debian Stable ± Flatpak gets best of both worlds
not just its origin, but the trackers embedded within:
https://reports.exodus-privacy.eu.org/en/reports/427597/#trackers
Settings / Audio & Video / Enable both: “Use HLS” and “LBRY HLS”
If your interested in a more private OS for your phone - I did some searching and unfortunately GrapheneOS won’t support the 3a anymore, and the DivestOS is broken for the 3a.
If your feeling up to it, I would recommend either CalyxOS or LineageOS:
Launch your browser.
Right-click on your toolbar to open toolbar settings.
Click on Customize Toolbar.
A new page with a list of items will open that you can drag into the toolbar.
Click on the Add-on and drag it into your toolbar.