How to enable Browser Alert on Firefox?

Condition

When executing tests in Katalon Studio, the expected alert does not appear in Firefox. This issue only occurs when running tests through Katalon; the alert displays correctly when testing manually. In contrast, Chrome and Microsoft Edge display the alert as expected both manually and through Katalon automation.

Cause

In Firefox, the dom.disable_beforeunload preference is set to true by default. This setting prevents the beforeunload event from triggering alerts, which explains why the expected alert is blocked during automated execution.

Solution

To resolve this issue, the dom.disable_beforeunload preference must be set to false before launching Firefox. This can be achieved by configuring Firefox through FirefoxOptions.

Since the Firefox driver constructor accepts only FirefoxOptions (and not generic DesiredCapabilities), the preference needs to be explicitly added before creating the driver instance.

Example

String browser = DriverFactory.getExecutedBrowser().getName();

if (browser.equalsIgnoreCase("FIREFOX_DRIVER")) {  
    System.setProperty("webdriver.gecko.driver", DriverFactory.getGeckoDriverPath());
    
    FirefoxOptions firefoxOptions = new FirefoxOptions();
    firefoxOptions.addPreference("dom.disable_beforeunload", false); // Required for Firefox
    
    WebDriver driver = new FirefoxDriver(firefoxOptions);
    driver.navigate().to(url);
    DriverFactory.changeWebDriver(driver);
} else {
    WebUI.openBrowser(url);
}

This ensures the alert is displayed in Firefox, consistent with other supported browsers.