Theseus had no content blocking at all. Shield blocks requests to known
tracking and advertising hosts on every site, using EasyList and
EasyPrivacy through Ghostery's adblocker engine (the matcher those lists
are written for). The lists ship inside the add-on so blocking works
from the first launch, offline; the compiled engine is cached under the
add-on's data dir (a 22 ms load instead of a 500 ms parse), and the
lists refresh from their publishers about once a day.
The panel shows what was stopped on the current page, a one-click
allow for the site, the global switch, the running total and the rule
versions with an "Update now". Network filters only for now: a blocked
request never leaves the browser, but leftover empty ad boxes are not
hidden yet.
Host side: a "request-filter" capability. Chromium allows one
onBeforeRequest listener per session, so main owns it and consults the
add-ons' filters; a top-level navigation is never blocked, only http(s)
subresources are offered. api.tabs (active tab and a change event) lets
the panel show per-site numbers without seeing page content.
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