Have had some problems playing Jacquie Lawson animations lately when received from friends. Found their suggestion to "refresh" the browser to bypass a cached item that may be the problem. For Firefox 48.0.2 my desktop Mini (OS 10.8.5), Cmd-R. Worked.
A Wikipedia article with more detail, https://en.wikipedia.org/wiki/...ache#Bypassing_cache
"For what is age but youth's full bloom,
A riper, more transcendent youth" - Oliver Wendell Holmes