Changing a single setting to speed up loading websitesTo increase number of downloads to more then 6 at once enter in Firefox's address bar:
and then look for value:about:config
which by default is 6. You can safely change this value to 20 or 30 to speed up websites.network.http.max-persistent-connections-per-server
However keep in mind that some servers might block you if you try to make too many parallel connections so increasing it to more than 30 is not encouraged.
I can recommend 30. With this value every website works perfectly.