I really can't blindly accept what the post says. A long time ago, in a version far far away, glibc started using mmap() on /dev/zero instead of brk() to allocate memory. This has the advantage that memory that is freed returns to the OS immediately and Linux is able to handle memory fragmentation better than Firefox itself (memory fragmentation on OS level is a very different thing). This means that there needs to be no free memory handling in any application, unless the app chooses to re-use its freed memory. But even in that case, fragmentation could be reduced by just freeing fragmented memory.

So, no. When judging languages leave the memory fragmentation out of the conversation and surely don't compare the memory handling of Java with the memory handling of Firefox. I'm 100% sure that the Llinux kernel can do much better than JVM since it has actual view of the physical ram and the actual page allocation.