Selenium test added (#906)

* add a selenium test for firefox

* add geckodriver and firefox to travis

* install updated

* install updated

* try out suggested webdriver dependency class

* add more resilience

.travis.yml

@@ -8,7 +8,10 @@ dist: xenial
 jdk:
   - openjdk11
   - openjdk15
-install: true
+addons:
+  firefox: latest
+install:  
+  - true
 script:
   - export BRANCH=$(if [ "$TRAVIS_PULL_REQUEST" == "false" ]; then echo $TRAVIS_BRANCH;
     else echo $TRAVIS_PULL_REQUEST_BRANCH; fi)