Mozilla’s automated builds of Firefox for Windows, macOS, Linux, and Android are all cross-compiled on Linux VMs. Cross-compiling is faster and cheaper, especially because Windows’ file I/O and process launching is so slow.
There's some documentation on this in some WSL issues on GitHub, but it's not just NTFS. It's stuff like the broader filesystem architecture's inclusion of pluggable 'filters' (kinda neat, but each layer of them incurs a performance cost) or the way commands on other operating systems depend on caches for certain syscalls that Windows doesn't keep, or keep anything equivalent to.
This one? I remember it as an earnest description of the difficulties the WSL team had with the speed of NTFS - and I think it was one of the reasons for the switch to virtualisation in WSL2.
My takeaway from that comment is that there are some important performances issues that apply generally to all filesystems on Windows. Maybe we can partially test whether that's the case by playing with WSL1 on ReFS, ExFAT (if that's even supported, with its limited permissions support, or ZFS, once OpenZFS on Windows stabilizes a bit.
