I have a client with an Imac- 10.10. I recently installed Apple Airport Extremes for improved wifi, removing a Netgear router. All other devices in the home have no issues. However on the Imac, browsers (used Safari AND Firefox) will work for a short period and then will not surf and leave the spinning wheel until it times out or just sits there and I have to force quit. This happens with wifi AND Ethernet connection. If you reboot the Imac, everything works again for a short period and then stops. I can ping anywhere without a problem. I have reset defaults on the browsers and still the same issue. I ran Malwarebytes and found the "seach protect" crapware on the system and removed it. However, still the same issue. I have also put the original Netgear router back in to see if possibly a compatibility problem of some sort, and it happens with the Netgear as well now.