It’s been a while since i mucked around with browser extensions, but i assume they don’t have network access by default. Surely there is an extension with page read access and without network access, no?
I don’t think that’s an accurate description of browser extensions. Content scripts work that way, and many browser extensions include content scripts… but not all browser extensions use content scripts.
Anyway, a quick readthru of the code of the extension i linked shows it does use content scripts, but also it doesn’t do any network access.