This might be an unpopular opinion here, but I don't begrudge sites the non-intrusive use of ads. If it doesn't drastically slow down the website or make the site unreadable, I accept that most sites have to use it to support themselves. I don't have the money to support a website with my own money, because I'm a broke teenager. :P But when I use
fivethirtyeight.com, for instance, I can accept a few non-intrusive ads around the site to make it so that the site can continue to exist without significantly slowing down its performance- I'm there to read for goodness' sake, it's not like I'm doing anything requiring high-tech performance anyway.
To summarize my ramblings: I'm grateful sites like lichess exist that don't use ads, especially when the service offered requires some high-speed stuff, like Bullet does. But I on't begrudge other sites use of ads, because I can't give money, but I don't really mind watching an ad or having a few ads on the side of the screen that don't significantly worsen my experience and help the creator fund their project.