get right firefox version for your selenium

 

find the selenium location path
 find / -name  selenium
output:  /usr/local/lib/python2.7/dist-packages/selenium

1. get the "webdriver.xpi" file, the file is under "/usr/local/lib/python2.7/dist-packages/selenium/webdriver/firefox"
2. unzip webdriver.xpi  to get one file, named "install.rdf"
3.  cat install.rdf, we will find one object "

   <!-- Firefox -->
   <em:targetApplication>
   <Description>
   <em:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</em:id>
   <em:minVersion>3.0</em:minVersion>
   <em:maxVersion>48.0</em:maxVersion>
   </Description>this means firrefox version should >=3.0 and  <= 48.0, 

4. select one firefox version you want to install/re-install, from ftp server: https://ftp.mozilla.org/pub/firefox/releases/
5. install/re-install firefox guide: https://www.askmetutorials.com/2016/06/install-firefox-47-on-ubuntu-1604-1404.html