Looks like that disables Servo at build time. Someone on Reddit had the same problem - https://www.reddit.com/r/firefox/comments/6p9t83/psa_you_can_try_out_styl

Looks like that disables Servo at build time. Someone on Reddit had the same problem - https://www.reddit.com/r/firefox/comments/6p9t83/psa_you_can_try_out_stylo_in_firefox_nightly_now/dknv93q/?context=4 https://www.reddit.com/r/firefox/comments/6p9t83/psa_you_can...