Ask HN: Contractor SWE vs. Full time SWE – your experience?

I was approached by a staffing agency for a contracting position at BigCorp. The staffing agency claimed that it will be a long term on-going contract. I have not been given any other specific details about the contract other than the pay and the number of weekly work hours. I have never worked as a software contractor in the past. For those who have experience in this field: 1. What is the difference between the work that a software contractor does vs a full time SWE? 2. What salary range should I expect? The salary that I am being offered(40hrs/wk) works out to the average SWE salary in the city acc to payscale. Your thoughts on anything else that I might be missing are appreciated.