Can't load more than 3 pinned tabs simultaneously

Hi, I've got 12 pinned tabs that load at Firefox start and need them to be pinned. Problem is Firefox loads only 3 tabs simultaneously, from left to right. Consequence it takes ages to load all of them and especially the last ones. I tried to find an about:config setting to mod this behavior, unsuccessfully. Settings I've already changed (x2): browser.tabs.remote.warmup.maxTabs 6 network.http.max-connections 2000 network.http.max-persistent-connections-per-proxy 34 network.http.max-persistent-connections-per-server 12 network.http.max-urgent-start-excessive-connections-per-host 6 Please could you point me to the correct setting ? Thanks a lot.