Add Firefox 45 workaround in ComboBoxElement (#8449)

testbench-api/src/main/java/com/vaadin/testbench/elements/ComboBoxElement.java

 import org.openqa.selenium.WebElement;
 
 import com.vaadin.testbench.By;
+import com.vaadin.testbench.TestBenchElement;
 import com.vaadin.testbench.elementsbase.ServerClass;
 
 @ServerClass("com.vaadin.ui.ComboBox")
     private boolean selectSuggestion(String text) {
         for (WebElement suggestion : getPopupSuggestionElements()) {
             if (text.equals(suggestion.getText())) {
-                suggestion.click();
+                clickElement(suggestion);
                 return true;
             }
         }
      */
     public boolean openNextPage() {
         try {
-            getSuggestionPopup().findElement(byNextPage).click();
+            clickElement(getSuggestionPopup().findElement(byNextPage));
             return true;
         } catch (WebDriverException e) {
             // PhantomJS driver can throw WDE instead of the more specific
      */
     public boolean openPrevPage() {
         try {
-            getSuggestionPopup().findElement(byPrevPage).click();
+            clickElement(getSuggestionPopup().findElement(byPrevPage));
             return true;
         } catch (WebDriverException e) {
             // PhantomJS driver can throw WDE instead of the more specific
             }
         }
     }
+
+    private void clickElement(WebElement element) {
+        if (isFirefox()) {
+            // Workaround for Selenium/TB and Firefox 45 issue
+            ((TestBenchElement) (element)).clickHiddenElement();
+        } else {
+            element.click();
+        }
+    }
 }