I too faced the same problem. I had the latest firefox browser and plugins. So tried clearing cookies and cache. But still it was horrible.
The trick for me was changing the browser. Tried with chrome and it improved a lot but still i faced the problem sometime.
Now I'm using Torch browser. Well it's working flawless for me. I recommend that you try it.

Regarding the phone issue i feel it happens when signal drops a lot. When connected to a good wifi hotspot i almost don't encounter the problem.

Hope it helps.