There are multiple (mostly technical) reasons for this termination, but the main two reasons are outlined below:
- Unlike Pale Moon 27.*, Pale Moon 28 does not build on CentOS 6.5. Later versions of CentOS use and build against later versions of libraries that won't run on older versions of the meta-distro for old hardware, Puppy Linux. These older versions of Puppy Linux are usually the only distro variants that can be used on the hardware in question.
- With version 28, the stdcxx_compat hack no longer works even for a partial build that fails at a later stage.
These two items alone require a somewhat newer distro that would most definitely struggle on a Pentium 3 CPU, and would simply not be in use on SSE-targeted machines.
As it stands, Walter will end his builds after v27 has seen its last maintenance release.
Of course there is the possibility for someone to step up and do an ESR fork of Pale Moon 27, specifically for older hardware, but be aware that you will have to port all relevant security bugs across every Firefox cycle for it to remain a viable fork.