I wouldn’t use any other extensions, especially something like Chamaleon for Mullvad browser though.
Extensions, specifically the ones that change how a website behaves or how a website sees the user (such as an adblocker or a user agent string switcher) can be detected. Mullvad only comes with NoScript and uBlock Origin which is enough most of the time, and installing other extensions can be used to fingerprint you, especially since Mullvad tries to have every user seem like the same user to websites (which is why things such as letterboxing are enabled).