I might recommend updating the operating system, however I could not reproduce this from a google.com search page for youtube videos. What exact steps are you taking, and do you have an example?

Thank you

if i do a search at google and then click on a link, ex. from an actual search;

https://www.youtube.com/watch?v=pn6QwzqgPic

.. the url as above appears briefly in the address bar, then changes briefly to ..

https://m.youtube.com/?client=mv-google

.. and then lands at ..

https://m.youtube.com/

If i copy the original link from google and paste it into Safari, the relevent video page loads as expected. This happens for any and all youtube links i try in Firefox.