load time differences between browsers

I’m working on a private instance of WebPagetest to which I associated with an execution system, and reading results…

one crontab module commands the execution of the tests with almost constant frequency, then the data collected can be displayed on the time graph.

the system is based on version 2.19.

this is the portion of code that launches the tests:
function launch_test() {

//location sintax is: name:browser.LAN

$url_completa = $this->url_server.“runtest.php?f=xml&location=”.$this->location."&fvonly=1&mv=1&ignoreSSL=1&video=1&script=".$this->script;
$ch = curl_init($url_completa);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_BINARYTRANSFER, true);
$output = curl_exec($ch);

$datatest = simplexml_load_string($output);


I’m doing tests with a probe so configured:

[]Windows 10
]Internet Explore 11
[]Chrome 49
]Firefox 45


browser=IE11, Chrome, Firefox
Time Limit=120
;Automatically install and update support software (Flash, Silverlight, etc)

exe=“C:\Program Files (x86)\Google\Chrome\Application\chrome.exe”
options=’–load-extension="%WPTDIR%\extension" --user-data-dir="%PROFILE%" --no-proxy-server’

exe=“C:\Program Files (x86)\Mozilla Firefox\firefox.exe”
options=’-profile “%PROFILE%” -no-remote’

;exe=“C:\Program Files\Safari\Safari.exe”

exe=“C:\Program Files\Internet Explorer\iexplore.exe”[/code]



label=“Pisa conf W10”

browser=IE11, Chrome, Firefox
user-data: wpt_server=

The following is an example of data collected by the probe test … Pisa1_T with three different browsers:

of course you can click on the points on the graph to see the details … the following two cases, one with IE11 and the other with Firefox:

I can not understand why IE11 run correctly onload event while chrome and firefox very often miss the event and show activity time instead of load time.

many thanks in advance for the help

OK, some things to look at…

If you do multiple runs for each test (say 3 minimum) do the outliers get smoothed out?

How often are those jpg’s taking so long to load?

If you compare a fast test and a slow test in the same browser what’s making the difference in speed?

I did not understand what you mean by multiple runs … each test is performed every 5 minutes as you can see from the chart, each time with a single run (&fvonly=1).

the images in the final part of the waterfall composing a slider and are downloaded through the use of timers javascript.

the fast test and a slow test in the same browser do not differ from the side user experiences … but the agent does not detect the onload event (in slow test case) and return the activity time instead (load time field in csv).

all tests are run on the same computer and the same agent