diff --git a/extensions/cookie/test/unit/test_bug481775.js b/extensions/cookie/test/unit/test_bug481775.js
new file mode 100644
index 000000000000..86dd1663513f
--- /dev/null
+++ b/extensions/cookie/test/unit/test_bug481775.js
@@ -0,0 +1,80 @@
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+
+function run_test() {
+  var cs = Cc["@mozilla.org/cookieService;1"].getService(Ci.nsICookieService);
+  var cm = Cc["@mozilla.org/cookiemanager;1"].getService(Ci.nsICookieManager2);
+  var ios = Cc["@mozilla.org/network/io-service;1"].getService(Ci.nsIIOService);
+  var prefs = Cc["@mozilla.org/preferences-service;1"].getService(Ci.nsIPrefBranch);
+  var pb = null;
+  try {
+    pb = Cc["@mozilla.org/privatebrowsing;1"].getService(Ci.nsIPrivateBrowsingService);
+  } catch (e) {}
+
+  // accept all cookies and clear the table
+  prefs.setIntPref("network.cookie.lifetimePolicy", 0);
+  cs.removeAll();
+
+  // saturate the cookie table
+  addCookies(0, 5000);
+
+  // check how many cookies we have
+  var count = getCookieCount();
+  do_check_neq(count, 0);
+
+  // if private browsing is available
+  if (pb) {
+    // enter private browsing mode
+    pb.privateBrowsingEnabled = true;
+
+    // check that we have zero cookies
+    do_check_eq(getCookieCount(), 0);
+
+    // saturate the cookie table again
+    addCookies(5000, 5000);
+
+    // check we have the same number of cookies
+    do_check_eq(getCookieCount(), count);
+
+    // remove them all
+    cs.removeAll();
+    do_check_eq(getCookieCount(), 0);
+
+    // leave private browsing mode
+    pb.privateBrowsingEnabled = false;
+  }
+
+  // make sure our cookies are back
+  do_check_eq(getCookieCount(), count);
+
+  // set a few more, to trigger a purge
+  addCookies(10000, 1000);
+
+  // check we have the same number of cookies
+  var count = getCookieCount();
+  do_check_eq(getCookieCount(), count);
+
+  // remove them all
+  cs.removeAll();
+  do_check_eq(getCookieCount(), 0);
+}
+
+function getCookieCount() {
+  var count = 0;
+  var cm = Cc["@mozilla.org/cookiemanager;1"].getService(Ci.nsICookieManager2);
+  var enumerator = cm.enumerator;
+  while (enumerator.hasMoreElements()) {
+    if (!(enumerator.getNext() instanceof Ci.nsICookie2))
+      throw new Error("not a cookie");
+    ++count;
+  }
+  return count;
+}
+
+function addCookies(start, count) {
+  var cm = Cc["@mozilla.org/cookiemanager;1"].getService(Ci.nsICookieManager2);
+  var expiry = (Date.now() + 1000) * 1000;
+  for (var i = start; i < start + count; ++i)
+    cm.add(i + ".bar", "", "foo", "bar", false, false, true, expiry);
+}
+
diff --git a/netwerk/cookie/src/nsCookieService.cpp b/netwerk/cookie/src/nsCookieService.cpp
index 63315ad573c4..a094929fa393 100644
--- a/netwerk/cookie/src/nsCookieService.cpp
+++ b/netwerk/cookie/src/nsCookieService.cpp
@@ -838,10 +838,10 @@ nsCookieService::PrefChanged(nsIPrefBranch *aPrefBranch)
     mCookiesPermissions = (PRUint8) LIMIT(val, 0, 2, 0);
 
   if (NS_SUCCEEDED(aPrefBranch->GetIntPref(kPrefMaxNumberOfCookies, &val)))
-    mMaxNumberOfCookies = (PRUint16) LIMIT(val, 0, 0xFFFF, 0xFFFF);
+    mMaxNumberOfCookies = (PRUint16) LIMIT(val, 1, 0xFFFF, kMaxNumberOfCookies);
 
   if (NS_SUCCEEDED(aPrefBranch->GetIntPref(kPrefMaxCookiesPerHost, &val)))
-    mMaxCookiesPerHost = (PRUint16) LIMIT(val, 0, 0xFFFF, 0xFFFF);
+    mMaxCookiesPerHost = (PRUint16) LIMIT(val, 1, 0xFFFF, kMaxCookiesPerHost);
 }
 
 /******************************************************************************
@@ -2130,6 +2130,7 @@ removeExpiredCallback(nsCookieEntry *aEntry,
 void
 nsCookieService::RemoveExpiredCookies(PRInt64 aCurrentTime)
 {
+  NS_ASSERTION(mDBState->hostTable.Count() > 0, "table is empty");
 #ifdef PR_LOGGING
   PRUint32 initialCookieCount = mDBState->cookieCount;
 #endif
@@ -2418,5 +2419,6 @@ findOldestCallback(nsCookieEntry *aEntry,
 void
 nsCookieService::FindOldestCookie(nsEnumerationData &aData)
 {
+  NS_ASSERTION(mDBState->hostTable.Count() > 0, "table is empty");
   mDBState->hostTable.EnumerateEntries(findOldestCallback, &aData);
 }