About an hour ago, I was using Firefox on my 2006 MacBook. It went something like this...
"You're version of Firefox is outdated. You should upgrade."
The newer versions didn't use to work on my MB because my OS was too old, but I figured that they must have changed something because they actually recommended upgrading (which they hadn't done before). Downloaded the version on Mozilla's site, installed it, and...it won't run on my Mac because my OS is too old. Grrr. Mozilla doesn't seem to have an easy way to find older versions, so I Googled it, found it, reinstalled what I already had, and then was able to use it.