I’m no expert but Google shows up results about Hijacks and serieous threats. Also there’s a lot of talk about specific add-ons. I suggest you try running firefox in safe-mode without any add-ons. If that helps, make a new profile your default and install add-ons one-by-one. If it doesn’t help and virusscanners/spywarescanners don’t solve it, take your time for a complete clean install.

It’s a legit Sun Java plugin. It’s up to you to let it enabled or not, depending on your surfing needs.

Thanks, @Ironbender . Now, what kind of “surfing needs” would the plugin fulfill?