Please how can I get my fans to stop running at maximum speed

I have a late 2011 15" MacBook Pro with 2.4 ghz i7 processors, 8 gb ram. I'm running the latest OS X 10.10.4 I find that my fans run long and a high rpm when I am working with Firefox, Skype, Acrobat, or other software in the background. I have repaired disks and permissions, and I have had the hardware tested at the Genius Bar. Everything tests just fine.

Often I find the computer slows down and I'm waiting for a process with a spinning disk that just hangs and hangs as the fans whine at high speed. It's like I lost half or more of the computing power. Activity monitor tells me I'm the CPU is working on clearing some kernel task, or Firefox or Skype are taking 120% or more of CPU power with only 15% of the CPU occupied with user tasks.

The change to run the fans longer and at higher rprm slowly came on over the last year, but it became more pronounced after I swapped my factory HD out and installed a 512 gb Cruz SSD.

Please what's wrong and what do I need to do to correct this?

Thanks so much.

J.