I went to the web site and had no problem.

Many site issues can be caused by corrupt cookies or cache.

• Clear the Cache and

• Remove Cookies Warning ! ! This will log you out of sites you're logged in to.

Type about:preferences in the address bar and press enter.

• Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
• Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now.

If there is still a problem, Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences in the address bar and press enter

Select Advanced > General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Then restart.

I followed your instructions but the problem remains.

Doesn't work for me either on Linux with Firefox 32. It works in Firefox 31

The Web Console (Firefox/Tools > Web Developer) shows this error.

Invalid URI. Load of media resource failed. happy

The MP3 seem to be crashing Firefox as I can't close and restart Firefox and need to kill the process.

I accidentally solved my own problem. What I need is an MP3 codec. step 1 - download an mp3 file, for example http://www.oxfordlearnersdictionaries.com/us/media/english/us_pron/h/hap/happy/happy__us_1.mp3

step 2 - play the mp3 file. It is likely that the media player will tell you to install an mp3 codec.

step 3 - install the mp3 codec

step 4 - restart Firefox

That was good work!