Dear Windows 10 Community,
while the issue I have experienced is not directly related to Windows 10, I hope that users who have encountered the same issue and think it might be related will see this and as such can correct it.
Current Build:
OS: Windows 10 64 Home Version 1511
Browser: Firefox 43.0.2
Network Adapter: Killer e2200 Gigabit Ethernet
Max Downloadspeed: 11 Mpbs
After my ugrade I had a serious issue with my internet slowing to a near standstill while any kind of download was happning that maxed my download speed. Since this did not happen with Windows 7, I naturally assumed that it was an aftereffect of the update. I tried google, but couldn't find anything that spoke about my exact issue, but other related topics so I tried these first:
I disabled the Windows 10 Peer-to-Peer function in hopes of it being the culprit, but to no avail.
At the same time, the "old drivers cause memory leaks"-issue popped up for me and some google answers said to update the network drivers, so I did - no change in either issues.
Maybe it had something to do with TCP (I remembered that I had done a TCP optimisation on Windows 7, but didn't exactly remember what it was for), so I tried that but alas still no change.
After all this failed, I decided to take a closer look at the Network adapter itself - I did not do this prior because I feared for crashing my internet completely as I am not the most tech-savy person when it comes to that part. There are two ways to reach your Network adapter properties.
Long way:
Start > Settings > Network & Internet > Ethernet > *Change adapter options > right-clicked the displayed adapter and chose "Properties".
Shot way:
Left-click your Network Icon in the Taskbar > choose "Network Settings" > See above at *
Inside the properties I saw a list described as "This connection uses the following items:" and one of those items was called "Qualcomm Atheros Bandwith Control" - which is a programm apparently installed if you have the same network adapter as me - and figured this might have something to do with my issue. I removed the checkmark and restarted my PC.
Now it works perfectly again! I can have a download running and still open google - or even watch a youtube video - without the connection either timing out or loading forever.
My conclusion:
After the update, a new driver for my Network adapter was installed that added this particular "feature" without my knowledge and thus started the whole issue. So while this is not directly related to Windows 10 itself, the update was the cause of it.
I hope that people who have the same issue as me will see this and it will hopefully help them.