Its not new and nor strange. It frequently happens whenever you continuously try to check SERPs or search queries. Generally it occurs when use IBP or any automated queries related to Google services. You should give at least 6 seconds gap between your searches. Google generally restore its service less than in an hour. You can avoid this error by using Google API.
If you do find that you're not sending your searches very quickly and have cleared your cookies but are still experiencing trouble, I suggest you make sure you don't have spyware on your computer, or a computer virus that allows others to surf off of your computer and make automated queries to Google. If you're unsure of a good spyware program, I can recommend one. And if you need help figuring out how to clear your cookies, I can help you out as well. Regards, Chana
Hmm...interesting. Do you have a lot of Add-Ons in Firefox? I'm curious if perhaps one of your Add-Ons could be causing it?
I also get this error, I think if we do searches too quickly then this error will generate. I also, use firefox. and sometimes, I get this error when I am not doing searches fast, strange