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Class C refers to the third set of numbers in an IP.
AAA.BBB.CCC.DDD
If all the links came from the same C subnet, they're 'likely' less trusted.
The 'theory' (calling it a theory because i don't think its ever really been proven) is that multiple links from the same C subnet are less valuable because its likely that they come from an owner of multiple websites.
I wouldn't label them as 'bad'
But if you're link building, it's probably a good idea to get links from different subnets 
I've never witnessed different results per browser.
Can you share your example keywords?
Make sure you're adding &pws=0 at the end of the url to make sure you're not getting any personalization.