Tony your problem is more than likely *not* the browser or plugin.
Most of these issues come from problematic UPnP support, double nat, or dual networks in house.... and some are even more bizzare requiring special commands to re-route packets to cross the wired lan/wireless lan bridge internal to your gateway firewall/router.
To start trouble shooting .. get your IP Address from a site like: whatismyip.com
Check that the IP address you have on your main home gateway wired/wireless firewall/router's *wan* or *internet* port. If the ip address is different then you have a network problem including double nat or 1 to 1 nat which would need additional info to help with.
After checking IP's.. need to know what your internet connection is (cable, dsl, broadband wireless, etc) and who provides it.
Need to know your Gateway devices ... brand & model (ie, 2wire DSL combo Modem/Routers .. looking those up, find they are not UPnP compatible.. etc .. that's what this info is being used for) .. same for your main network gateway.. someone posted they are using a Netgear 3700, some have more than one.. need to know what you have etc..
I recall you've got it wired directly to your gateway (that's good, no bridges, no homeplug adapters?) etc..
Next, confirm you've got the current firmware on those devices ... if you're using alternative firmware like DD-WRT/OpenWrt/Tomato.. then that is super important..
I always recommend setting up Static DHCP assignments for devices that shouldn't "move" and recommend they be Outside your normal dhcp range. most routers do "50" ip assignements from 2 to 50, or 100 to 150 ..etc.. I recommend static DHCP from 250 down.
ie. 722k -> 192.168.x.250, IPTV device: 192.168.x.249, Bluray .. 192.168.x.248 ...etc.. static DHCP means never having to try to manually assign inside a menu or having gamers thumb for all the button presses.
Lastly.. once on a Static DHCP for your router, if UPnP is the issue.. you'd create static port forwards for 5101 to the sling receiver. If you have more than one.. you'd have to create port forwards for each, 5101, 5102, 5103 ...
If all that sounds "easy" for you.. UPnP issue, static dhcp .. then try that first and then get back with the details on the products.... I would note, one person, not sure of his complete setup, found out by going device to device that someone had configured one of the computers with the same IP as his main gateway (192.168.1.1) and that was causing some of the problems for him. So getting to know your network and the devices in it... is a good thing..