We have a cache in the Resist Fingerprinting module that is somewhere between 3 and... 5(?) KB. (45 entries of 3 8-byte ints and one 32-byte string stored in a nsCString.) https://searchfox.org/mozilla-central/rev/a80651653faa78fa4dfbd238d099c2aad1cec304/toolkit/components/resistfingerprinting/nsRFPService.cpp#145 It's used to avoid performing a SHA256 when we can avoid it. 45 entries in the cache was chosen mostly arbitrarily based on the notion that "More is better, but much more than this didn't make any real Talos improvement." With Fission, we'll have fewer timelines per process so it's likely we could easily reduce this cache, possibly cutting it in half or more.