diff --git a/application/basilisk/app/profile/basilisk.js b/application/basilisk/app/profile/basilisk.js
index bb2e345df8..80a7127652 100644
--- a/application/basilisk/app/profile/basilisk.js
+++ b/application/basilisk/app/profile/basilisk.js
@@ -923,6 +923,11 @@ pref("dom.ipc.shims.enabledWarnings", false);
 // Start the browser in e10s mode
 pref("browser.tabs.remote.autostart", true);
 pref("browser.tabs.remote.desktopbehavior", true);
+pref("browser.tabs.remote.ignoreBlockPolicy", true);
+// -1 means automatic tab-isolation mode: try one process per tab.
+pref("dom.ipc.processCount", -1);
+// Safety ceiling used by automatic tab-isolation mode.
+pref("dom.ipc.processCount.webIsolatedMax", 64);
 
 // This pref governs whether we attempt to work around problems caused by
 // plugins using OS calls to manipulate the cursor while running out-of-
@@ -1245,10 +1250,8 @@ pref("browser.tabs.remote.autostart.2", true);
 pref("extensions.interposition.enabled", true);
 pref("extensions.interposition.prefetching", true);
 
-// Enable blocking of e10s for add-on users on beta/release.
-#ifdef RELEASE_OR_BETA
-pref("extensions.e10sBlocksEnabling", true);
-#endif
+// Keep e10s enabled even when legacy add-ons are present.
+pref("extensions.e10sBlocksEnabling", false);
 
 // How often to check for CPOW timeouts. CPOWs are only timed out by
 // the hang monitor.
diff --git a/dom/ipc/ContentParent.cpp b/dom/ipc/ContentParent.cpp
index 6dab0bbc82..8577af7b8c 100644
--- a/dom/ipc/ContentParent.cpp
+++ b/dom/ipc/ContentParent.cpp
@@ -574,6 +574,7 @@ ContentParent::GetNewOrUsedBrowserProcess(bool aForBrowserElement,
 {
   nsTArray<ContentParent*>* contentParents;
   int32_t maxContentParents;
+  bool preferDedicatedProcess = false;
 
   // Decide which pool of content parents we are going to be pulling from based
   // on the aLargeAllocationProcess flag.
@@ -591,13 +592,20 @@ ContentParent::GetNewOrUsedBrowserProcess(bool aForBrowserElement,
     contentParents = sBrowserContentParents;
 
     maxContentParents = Preferences::GetInt("dom.ipc.processCount", 1);
+    if (maxContentParents == -1) {
+      // Automatic mode: create a dedicated content process per new tab until
+      // a safety ceiling is reached, then reuse existing processes.
+      preferDedicatedProcess = true;
+      maxContentParents = Preferences::GetInt("dom.ipc.processCount.webIsolatedMax", 64);
+    }
   }
 
   if (maxContentParents < 1) {
     maxContentParents = 1;
   }
 
-  if (contentParents->Length() >= uint32_t(maxContentParents)) {
+  if (!preferDedicatedProcess ||
+      contentParents->Length() >= uint32_t(maxContentParents)) {
     uint32_t maxSelectable = std::min(static_cast<uint32_t>(contentParents->Length()),
                                       static_cast<uint32_t>(maxContentParents));
     uint32_t startIdx = rand() % maxSelectable;
diff --git a/toolkit/xre/nsAppRunner.cpp b/toolkit/xre/nsAppRunner.cpp
index 25ba3528d6..c04b8f6034 100644
--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -4203,6 +4203,12 @@ MultiprocessBlockPolicy() {
   }
   gMultiprocessBlockPolicyInitialized = true;
 
+  // Allow downstream applications to bypass legacy e10s block policies.
+  // This is evaluated at startup and requires restart to take effect.
+  if (Preferences::GetBool("browser.tabs.remote.ignoreBlockPolicy", false)) {
+    return gMultiprocessBlockPolicy;
+  }
+
   /**
    * Avoids enabling e10s if there are add-ons installed.
    */