“Orthodox Jews, for example, don’t start fires on the Sabbath but do use pre-existing fires. Karaites prefer to sit in the dark and freeze.”
I had a really good friend who was Karaite in Israel. He would go to the breaker box and turn off the power to his condo (did not want to “buy” electricity).
People whack on them as apostate, but, in practice, they end up well within Orthodox practices (except with dairy/meat issues and a few others).
I have the greatest respect for Karaites, but I wouldn’t say they are “well within Orthodox practices.” There are just too many theological and practical differences.