It denies resource:// access to Web content, it can help defend against fingerprinting.
PureOS should include Mozilla addon [[https://notabug.org/desktopd/no-resource-uri-leak/|no-resource-uri-leak]] and install it by default, to limit leaking fingerprints.
Debian tracks creation of package no-resource-uri-leak at [[https://bugs.debian.org/869654|bug#869654]].
When done, that package should be included in the default set in calamares and debian-installer.