Check if Firefox > 52.02 will solve memory problems

[toschneck]

Since the new version of firefox 52.02, it reserves a lot of not needed memory. See https://github.com/ConSol/sakuli/issues/276

Temporary solution: go back to previous firefox 45

TODO: Try later again to fix this issue command to validate memory usage: ps -o rss= -p <pidof> | awk '{print $1*4/1024, "MiB"}'

[toschneck]

Tested today version 58.0b4 still not respecting cgroups and reserves a lot of memory. So will keep firefox 45 for now.