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, 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.

Over 50 cookies! If I delete them all wont that screw up pc? some cookies are: face book.com,you tube.com,yahoo.com etcetc! And thank you for help.

You only need to delete cookies from those sites giving you problems. Also, web sites will re-create any cookies they need. The only real harm is your log-in information will be lost.

You can check for problems with current Shockwave Flash plugin versions and try this:

• check for updates for your graphics drive drivers
  https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration
• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)
• disable hardware acceleration in the Flash plugin

See also:

• http://kb.mozillazine.org/Flash#Troubleshooting

In Firefox 35 you can toggle this pref to true on the about:config page to disable protected mode in the Shockwave Flash plugin.

• dom.ipc.plugins.flash.disable-protected-mode = true
• http://www.ghacks.net/2014/12/21/how-to-disable-flash-player-protected-mode-in-firefox/

Blue screen crashes nearly always involve an incompatibility with low level system software, usually video/display driver software, but occasionally audio driver software.

As mentioned in cor-el's post, but you can bypass the display driver software by disabling both Firefox and the Flash plugin from using hardware acceleration. I'm not sure there is a way to bypass audio driver software. Hopefully it won't come to that...