Firefox

Sorry to say, but that design is quite intentional. If you stretch webpages too wide, it makes it difficult to read any texts, since finding the start of the next line is rather challenging then.

And if they'd re-layout it to place multiple settings elements next to each other, that would add quite a lot of visual complexity, it would make it harder to explain to people where they find a particular setting and well, just more effort for designing/maintaining that page.