An add-on's storage.get read and parsed its whole store file on every call,
and storage.set read, parsed and rewrote it — synchronously, on the main
thread. Traced on a real profile (installed 0.3.70): with a 7.5 MB Aegis
store, 30 of the first 35 s of main-thread time went to storage.get, the
window sat in "Not Responding" from 3 s to 19 s, and the first page showed at
19 s. One get cost ~73 ms; Aegis does dozens per state update.
lib/addon-store.cjs keeps one in-memory copy per store, shared by the
add-on's api.storage (addons-host.js) and its pages (addon-storage-* IPC in
main.js). After a one-time load a get costs microseconds; values are copied
in and out (structuredClone), so callers keep the old semantics. Writes are
coalesced (100 ms) and land as temp-file + rename, and are flushed on quit;
a store that doesn't parse is moved aside instead of being replaced by {}.
Measured on copies of the same profile, dev build:
first page 16.9-17.6 s -> 1.5-1.7 s; main thread blocked 24.7-25.8 s of
30 -> 1.0-1.1 s; longest freeze 13.7-15.0 s -> 0.6 s.
The Aegis side (capping its unbounded txCache) ships separately through
Aegis's own update channel. The boot tracer gains total/longest block columns.
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