My biggest gripe about Firefox OS was that Mozilla partnered with companies making low end phones that were quite awful even for that time. At that time, I felt that if it were released with high end or near high end hardware, the overall user experience would've have been much better and there would've been more freedom for Mozilla to focus on the important things. It could've then percolated down to cheaper/low end hardware with a separate "make Firefox OS lean" program. Trying to compete with Android on devices that were underpowered, in my view, killed all prospects of it surviving.