Windows 10 web access

[#1]

Installed Windows 10, access to internet (Firefox) and news groups often very slow. Webpages address needed to be refreshed several times. Access to f9 and Mozilla newsgroups via Thunderbird often  timed put. Tried several things but what worked in the end was to change 'Obtain server DNS automatically' to 'use the following DNS server addresses. 212.159.13.49,and 50'. Now load at the speed I would expect.
Can anybody explain?

[#2]

Perhaps your network driver was not working as it should?  It probably got changed as part of the update process.