Stick out to who? Just set the useragent to a default firefox one (assuming its not already set) and you're golden.
Mozilla/5.0 (Windows NT 10.0; rv:102.0) Gecko/20100101 Firefox/102.0
On my Firefox:
Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:109.0) Gecko/20100101 Firefox/110.0
It's interesting to note that the Mullvad browser seems to be based off on Firefox 102.0, which came way back on June 28, 2022: