I had the same issue with firefox 38.
After using following version dependencies, I could resolve the issue.
<dependency>
<groupId>org.seleniumhq.selenium</groupId>
<artifactId>selenium-java</artifactId>
<version>2.53.0</version>
</dependency>
<dependency>
<groupId>org.seleniumhq.selenium</groupId>
<artifactId>selenium-firefox-driver</artifactId>
<version>2.53.0</version>
</dependency>