Bug 1667913 - Enable incremental weakmap marking in the browser r=jonco

Differential Revision: https://phabricator.services.mozilla.com/D91665

modules/libpref/init/all.js

@@ -1149,6 +1149,9 @@ pref("javascript.options.mem.max", -1);
 pref("javascript.options.mem.gc_per_zone", true);
 pref("javascript.options.mem.gc_incremental", true);
 
+// JSGC_INCREMENTAL_WEAKMAP_ENABLED
+pref("javascript.options.mem.incremental_weakmap", true);
+
 // JSGC_SLICE_TIME_BUDGET_MS
 // Override the shell's default of unlimited slice time.
 pref("javascript.options.mem.gc_incremental_slice_ms", 5);