I see a lot of people asking for a light distro and then they are disappointed because the performance is not what they expected. When you use a modern browser, your lightweight distro doesn't matter anymore. The web stack is heavy, even if sites are coded with performance in mind.
I repurposed an old laptop for occasional video watching, running a small debian. Firefox or chrome are huge compared to everything else.
The other factor is that high video resolution eats the machine.
youtube-dl (480px) + mpv is much nicer than streaming in a browser.