One computer I looked at had the time set to 2007. Therefore, it ran into all kinds of certificate errors and you couldn't even get on YouTube. However, once the time was fixed, everything worked fine. Note, I also did a reinstallation of Firefox, but they might not have been necessary.
The time was corrected by simply adjusting the time display in the bottom right of the screen, no need for advanced work. For some reason, the owner didn't notice the wrong time, but she wasn't very tech savvy.