I would say that Flash is the plugin needed, not Java.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. '''Disable All of them.''' Can you post the web link(s) to those pages? 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'''<Enter> in the address bar. * '''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, '''[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; Type '''about:preferences#advanced'''<Enter> in the address bar. Under '''Advanced,''' Select '''General.''' Look for and turn off '''Use Hardware Acceleration'''. Poke around safe web sites. Are there any problems? Then restart.