According to Mozilla's statistics, 0.01% amounts to only 80'000 browser installs that use live bookmarks. That's not a big number and it's easy to find features that more people care about (ie multi-tab selection).
When resources are constrained you have to make decisions about what features you'll continue to develop and which to cut out. Live bookmarks was cut out. Mozilla devs have also mentioned that this feature is ancient code and would have required a lot of coding effort to bring up to date.
I'm sure if you were to invest the time to reimplement live bookmarks with modern code and with the internal restructuring in the browser in mind and you'd volunteer to maintain it and fix all filed bugs, they'd accept it.
When resources are constrained you have to make decisions about what features you'll continue to develop and which to cut out. Live bookmarks was cut out. Mozilla devs have also mentioned that this feature is ancient code and would have required a lot of coding effort to bring up to date.
I'm sure if you were to invest the time to reimplement live bookmarks with modern code and with the internal restructuring in the browser in mind and you'd volunteer to maintain it and fix all filed bugs, they'd accept it.