None of the quota APIs return a "remaining quota" value; they all return usage and quota (i.e. total of used + available).

window.webkitStorageInfo.queryUsageAndQuota(TEMPORARY, (used, quota) => {
  console.log(used, quota);
});

navigator.webkitTemporaryStorage.queryUsageAndQuota((used, quota) => {
  console.log(used, quota);
});

navigator.storageQuota.queryInfo().then(info => {
  console.log(info.used, info.quota);
});

navigator.storage.estimate().then(estimate => {
  console.log(estimate.usage, estimate.quota);
});

I should clarify - I'm resolving as "WontFix" assuming there's a misunderstanding about what the "quota" value returned means and that everything is working as intended. If I'm wrong, please comment and we can re-open!