Copied some time ago from a link on this site:
Type about:config in the address bar and press Enter.
Enter network.http in the filter field. Now make the following changes:
In the field of 'Preference Name' choices (click on the thumbnail at right to see the screen), double-click network.http.pipelining to set it to 'true'.
Next, double-click network.http.pipelining.maxrequests to bring up the 'Enter integer value' dialog box. Enter a higher number than the default 4; 15 works for me. Press Enter.
Double-click network.http.proxy.pipelining to set it to 'true'.
Right-click anywhere on the page and select New, Integer. Enter nglayout.initialpaint.delay and press . Set its value to 0 (zero), and press again.