software/seleniumserver,seleniumrunner: workaround firefox >= 60 font issue

This makes firefox 60 and 68 able to load some fonts and fixes the issue
that fonts were rendered as garbled text
1 job for fix/selenium_font in 0 seconds
Status Job ID Name Coverage
  External
failed SlapOS.SoftwareReleases.IntegrationTest-Jerome-736

08:01:59