I have a limited monthly bandwidth allowance. 240p is almost always "good enough" for me (and if there isn't any on-screen text even 144p is usually sufficient).
When I'm on the YouTube.com website, it respects my preferences (well, usually; sometimes there isn't a version that low quality, when that happens it chooses a medium quality from the available range).
Is there any way to force embedded clips on sites that I do not control to also respect my preferences? Quite often they present much higher resolution, and by the time I've noticed they've already buffered the rest of the clip anyway so changing manually doesn't help.