Please check if all your plugins are up-to-date. To do this, go to the [http://mozilla.com/plugincheck Mozilla Plugin Check site]. Once you're there, the site will check if all your plugins have the latest versions. If you see plugins in the list that have a yellow ''Update'' button or a red ''Update now'' button, please update these immediately. To do so, please click each red or yellow button. Then you should see a site that allows you to download the latest version. Double-click the downloaded file to start the installation and follow the steps mentioned in the installation procedure.

I have already checked the plugins and they're all up to date