There are software systems which do get updated while running though, but perhaps it requires a change in software architecture more than just (very clever) dif

There are software systems which do get updated while running though, but perhaps it requires a change in software architecture more than just (very clever) diff tools. Erlang systems, for instance, can have the concept of hot code swapping baked in to them in a more predictable way because that requirement is part of the base system - application life cycle is built in to the platform, not on top of it. Of course, for systems such as telecoms switching, the complexity and cost of this was worthwhile. For browsers... perhaps not. Cost/Benefit analysis is probably the usual trusted friend. What would we hope to gain (and how would we measure it) by letting browsers never restart?