Just got this message. Do I have malware?

[primarycolors]

This came up while I was doing some work and switched over to my browser.
I'm using Firefox on 10.9.5 Mavericks.

I obviously closed the prompt, but what does this indicate? What do I need to do?

 

[keysofanxiety]

1) Don't worry.
2) Err on the side of caution and run MWB for Mac: https://www.malwarebytes.com/mac-download/