--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -793,22 +793,16 @@ pref("browser.sessionstore.restore_on_de
 pref("browser.sessionstore.restore_hidden_tabs", false);
 
 // allow META refresh by default
 pref("accessibility.blockautorefresh", false);
 
 // Whether history is enabled or not.
 pref("places.history.enabled", true);
 
-// The percentage of system memory that the Places database can use.  Out of the
-// allowed cache size it will at most use the size of the database file.
-// Changes to this value are effective after an application restart.
-// Acceptable values are between 0 and 50.
-pref("places.database.cache_to_memory_percentage", 6);
-
 // the (maximum) number of the recent visits to sample
 // when calculating frecency
 pref("places.frecency.numVisits", 10);
 
 // buckets (in days) for frecency calculation
 pref("places.frecency.firstBucketCutoff", 4);
 pref("places.frecency.secondBucketCutoff", 14);
 pref("places.frecency.thirdBucketCutoff", 31);