This may be overkill, but hopefully it will help someone. Earlier, I reported a problem playing YouTube videos. Here's the solution I got from tech support. It worked like a charm and took two seconds. Two givens, though: You must use the native browser (not Dolphin or Opera Mini), and you must be using the mobile site, www.m.youtube.com
To access YouTube through the browser, [you] will need to set the browser mode itself to mobile. While in the browser, press the "Menu" button; then select "More" > "Settings." Scroll to the bottom of this list and uncheck the box beside "Browser Mode" to switch to mobile mode. You may need to reload the page after changing this setting.