--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -3357,16 +3357,19 @@ pref("dom.ipc.scheduler.chaoticSchedulin
 pref("svg.disabled", false);
 
 // Override default dom.ipc.processCount for some remote content process types.
 pref("dom.ipc.processCount.webLargeAllocation", 10);
 
 // Enable the Large-Allocation header
 pref("dom.largeAllocationHeader.enabled", true);
 
+// Disable e10s for Gecko by default. This is overridden in firefox.js.
+pref("browser.tabs.remote.autostart", false);
+
 // Pref to control whether we use separate content processes for top-level load
 // of file:// URIs.
 pref("browser.tabs.remote.separateFileUriProcess", true);
 
 // Pref that enables top level web content pages that are opened from file://
 // URI pages to run in the file content process.
 // This has been added in case breaking any window references between these
 // sorts of pages, which we have to do when we run them in the normal web