When trying out an upload implementation with different browsers, we noticed that firefox where slower than other browsers. We tried other services to see if it was only our implementation that where faulting, but saw the similar lock to 10mbit/s upload speed to youtube, google drive etc. Googling the issue didn't show any solutions or anyone having the same issue, but we had 3 computers with the issue, 2 Mac and one with Windows 10, latest versions of FF. We managed to find a setting in about:config called "network.http.spdy.send-buffer-size" and bumped it to 12582912 (same as network.http.spdy.pull-allowance, dont ask me why), default 131072, and this increased the upload speed to approximately 40mbit/s. Why is there a limit? Old firefox versions does not seem to have this limit.