I have Firefox 55.0.3 running on Mac OS X 10.11.6. Firefox takes extremely long to load Google sites (e.g., Gmail, fonts.googleapis.com calls from other websites), often timing out after delaying for more than 30 seconds. The problem does not occur with other browsers like Chrome. The problem is usually worst after waking the computer from sleep with Firefox still running, but quitting Firefox and restarting does not always fix the problem.