How can i resolve insecure connection on mozilla firefox 54 in selenium

I have used Selenium 3.4 along with Geckodriver v0.18.0.

To handle the SSL certificates in Firefox I used capabilities of Selenium Webdriver:

ProfilesIni profile = new ProfilesIni();
FirefoxProfile myprofile = profile.getProfile("default");
myprofile.setAcceptUntrustedCertificates(true);
myprofile.setAssumeUntrustedCertificateIssuer(false);
driver = new FirefoxDriver(myprofile);

But still it is showing an insecure connection after firefox launch

Here is the Answer to your Question:

As per the question without any reference to the url where the SSL certificates are blocking, here is the minimum code block to bypass the SSL Certificate. In this code block we will use the DesiredCapabilities Class to set the CapabilityType of ACCEPT_SSL_CERTS to true as follows:

package certificateIssue;

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.openqa.selenium.remote.CapabilityType;
import org.openqa.selenium.remote.DesiredCapabilities;
import org.testng.annotations.Test;

public class CertificateIssue_Firefox 
{

    @Test
    public void handleCertificate()
    {
        System.setProperty("webdriver.gecko.driver", "C://Utility//BrowserDrivers//geckodriver.exe");

        DesiredCapabilities cap= new DesiredCapabilities();
        cap.setCapability(CapabilityType.ACCEPT_SSL_CERTS, true);

        WebDriver driver = new FirefoxDriver(cap);
        driver.get("http://www.cacert.org/");

    }
}

Let me know if this Answers your Question.