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Firefox Send Buffer


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I noticed that on my computer Firefox by default sets the TCP send buffer equal to 128 KB (about:config -> network.tcp.sendbuffer), which limits the result of a single thread upload test. System default receive buffer is used, so download speed isn't affected. This value is adequate for normal web browsing and uploading to geographically close servers, but cannot be used to measure the best possible performance of bulk file transfers across different applications. Usually software don't set custom buffer sizes, or if they do, they use extreme values (FileZilla uses 4 MB).

I observed the following throughput with FireFox - 128 KB:


384 KB:


512 KB:



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Although my LTE connection is limited to about 16Mbps up, it did make a noticeable difference here also:


Default (131072) and after (524288):

F7nJDbY3I.png hVXmWjJg3.png


The Android Firefox does not seem to have this setting, however, I have noticed it has been producing faster upload results than Firefox on my PC, so it probably uses a larger send buffer by default.  It consistently produces faster upload results than the Chrome App, which seems to cap out about 12Mbps. 

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