Sync, Pocket, Dev tools, Screenshots etc are not required to display and interact with HTML pages. They are useful and it's nice they exist, but I don't see a reason to have them installed if I don't need them - just as I don't install every package available in OS just in case I'll need later it.
Even if they don't use resources when not being actively used (no way to test since there is no way to remove them), they increase attack surface and clutter UI.
There are users who value OSes where things are "just working", out of the box. Even more, there are users who value if OS has lots of stuff pre-installed.
There are users who value OSes for being absolutely minimal, so they can install only the stuff they want.
There are users who build their OSes from scratch, compiling each piece from source, fine-tuning every option they want to touch, manually defining every aspect of their system.
None of those approaches are wrong. And each of users may voice their discontent if things are not the way they prefer them to be (and that's good).
> But your OS does come with lots of packages and features you may not use.
Sure does. And I can remove them if I want to. I can apt-get remove libc6 if I really really want to and I accept the consequences. I can't remove non-essential parts of the Firefox, though.
Delete /usr/lib/firefox/browser/features/firefox@getpocket.com.xpi (or - better - rebuild the .deb package to not include this file) and the Pocket will be gone. Same for screenshots@mozilla.org.xpi.
Sync and DevTools are tightly integrated, though. I'd really really wish it would be realistically possible to remove Sync and replace it with something else.
Even if they don't use resources when not being actively used (no way to test since there is no way to remove them), they increase attack surface and clutter UI.