Greasy Fork is available in English.
Speed up, slow down, advance, rewind, loop any HTML5 video on any site with quick shortcuts!
The script always works. I use it myself every day :)
Regarding the default speed, if it’s still relevant to you, write here, I’ll think about what can I do.
Not working.
But would be great if it would save the default speed-setting, for me would be 2x :-)