Why my internet connection acts strangely?

I think this problems occurs due to poor net connectivity because as you told your system configuration it was good, but may be your internet service provider didn't give you better service so you face these problems. Either change your connection to Airtel or Tata or put a complaint. On the other hand you may also format your windows before change the Internet Provider. Please do not update latest versions of Mozilla as they crash more frequently, this is my personal experience. I always use mozilla 3.0 and disabled its updates. Try these options may be your query will solve.