Some videos and other websites no longer work in Firefox but still OK in internet explorer

Question

In Firefox, when I click on some YouTube videos, I get an errot message. The same link works fine in internet explorer.
The NY times Kenken puzzle page, http://www.nytimes.com/ref/crosswords/kenken.html?8qa&_r=0
no longer comes up properly, none of the puzzle links appear on screen. that website is fine in Internet Explorer.
A week ago, both worked fine.

Answer 1

Many site issues can be caused by corrupt cookies or cache.
* Clear the Cache
'''[https://support.mozilla.org/en-US/kb/how-clear-firefox-cache?redirectlocale=en-US&redirectslug=clear-cache-delete-temporary-files-fix-issues How to clear the Firefox cache]''' {web link}
and
* Remove Cookies
''This will log you out of all sites you're logged in to. ''
Press the '''<Alt>''' or '''<F10>''' key to bring up the tool bar.
Followed by;
Windows; '''Tools > Options'''
Linux; '''Edit > Preferences'''
Mac; ''application name'' '''> Preferences'''
Then '''Privacy.'''
Under '''History''', select Firefox will '''Use Custom Settings'''.
There is a button on the right side called '''Show Cookies'''.
If there is still a problem,
'''''[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Start Firefox in Safe Mode]''''' {web link}
While you are in safe mode;
Press the '''<Alt>''' or '''<F10>''' key to bring up the tool bar.
Followed by;
Windows; '''Tools > Options'''
Linux; '''Edit > Preferences'''
Mac; ''application name'' '''> Preferences'''
Then '''Advanced > General.'''
Look for and turn off '''Use Hardware Acceleration'''.
Poke around safe web sites and see if there is still a problem. Then restart.