I think that the maintainer should provide the instructions on how to patch the code of any (current) version of Firefox or its forks to build a version compatible with older Windows

[Sevoos]

It's ok that life requires time and effort, but it's always better to play safe - nobody knows what happens tomorror - take a look at vxiiduu, the former developer of VxKex. I believe that your guide is going to help a lot, while my knowledge isn't advanced enough.