I don't think Firefox uses meaningfully more energy due to "optional features", but rather due to simply not optimizing for battery efficiency at the same level that Apple does for Safari.

That type of optimization requires tons of profiling and is less glamorous than implementing new features, so I could see how it's hard to prioritize for Mozilla, especially if optimizations might look very different across OSes.

> rip nearly every feature out of Firefox and move it to “official extensions” that you can install optionally.

Only if they properly maintain those APIs. I'm still salty that they had tab groups, then broke that feature out to an extension, then killed the extension. (Then, much later, recreated the feature over again)

But yes, if done well modularity is probably good from a development perspective too.

I’m salty that at some point the Firefox interface became laggy on a state of the art 3GHz laptop when it wasn’t laggy in the past on a 400Mhz machine.

It doesn’t look all that different to how it did back then.