I tried to download a file and got this error message so I researched it to configure my connection limit and it told me to type "about:config" in the address bar and a page would open up that said "Advanced Preferences". I didn't get that page but I got a page with a long list of things I didn't understand. But I did find "http.max-persistent-connections-per-server" which was set at 6. I changed it to 10. I don't know if I did the right thing and I don't know if it helped. I couldn't find a way to configure my connections in Firefox Preference Settings. I've never ever had problems downloading files or multiples files at the same time. Did I do the right thing or is there something else I should do? I'm using Windows 10 and Firefox is up-to-date.