src/Process/SeleniumProcess.php
public function start($background = false)
    {
        $command = $this->getCommand();
        if (! $background) {
            exec($command);
            return $this;
        }

        $descriptors = $this->getDescriptorSpec();
        $this->process = proc_open($command, $descriptors, $this->pipes);
        return $this;
    }
public function start($background = false)
    {
        $command = $this->getCommand();
        if (! $background) {
            exec($command);
            return $this;
        }

        $descriptors = $this->getDescriptorSpec();
        $this->process = proc_open($command, $descriptors, $this->pipes);
        return $this;
    }
{@inheritdoc}

@return $this