There are some useful sandboxing features in Ubuntu's Linux 3.13 kernel series that we'd like to use. These kernels are associated with the Ubuntu 14.04 LTS ("Trusty") release train, but they are also supported with 12.04 LTS ("Precise"), and in fact a new install of 12.04 will use them. However, a host originally installed as 12.04.0 or 12.04.1 and then updated along the 12.04 train will not, and will remain on the 3.2 kernels (until April 2017, when 12.04 is EOLed). The hosts we're using for Linux Firefox automation appear to be in this last category, meaning that I'd be committing code that won't get test coverage on automation. This isn't the end of the world, but it would be nice to have an idea how long it might continue to be the case. Ubuntu's kernel release management is explained in more detail at https://wiki.ubuntu.com/Kernel/LTSEnablementStack The last time I asked about this on IRC, there were no concrete plans yet for moving the Linux test hosts to a newer version of Ubuntu. This is where all the verbiage about kernel version vs. the userland version comes in, because it's basically only the kernel that matters for sandboxing, and that may be sufficiently less work / lower risk as to be more likely to happen.

We are discussing starting work on moving from 12.04 -> 14.04 in Q2.