Facebook uses some elements of Java for some of its stuff. Unfortunately when it does this, you are kind of in a bind with 10.6.8, since its Java is not supported nor current anymore. Disable Java to avoid it thinking you might have what you don't.
Before upgrading to consider the most current Java, you must make sure everything is at least 10.7.3 compatible:
Thanks so much for responding! I googled 'how to disable Java MacBook Pro' and got a site that directed me to go to my browser's preferences drop down (my browser is Firefox), select content and find and uncheck 'Java Script". Unfortunately, there isn't anything about Java in the content section in Firefox preferences. Any ideas where to find it to disable it?