iMac downloads stall
I have an iMac 21.5, Late 2013 model / corei5 / 8GB memory. I have had the iMac for about 3 weeks now - new. I am having an issue downloading. It appears that downloads stall - just stops! I am connected thru wifi to my Comcast router. I have Dell laptop that is connected to the same router that has no issue downloading at all. It is also connected wireless. I changed my iMacs DNS to 8.8.8.8 and it worked for one download. It appears that this only happens when I use a web browser - safari, firefox. I used a download manager and downloads work just fine. Any suggestions??
iMac (21.5-inch, Late 2013), OS X Yosemite (10.10.2)