For #2110 - Pressing back on external link should close the tab

app/src/main/java/org/mozilla/fenix/browser/BrowserFragment.kt

@@ -555,10 +555,18 @@ class BrowserFragment : Fragment(), BackHandler, CoroutineScope {
             readerViewFeature.onBackPressed() -> true
             customTabsIntegration.onBackPressed() -> true
             sessionFeature.onBackPressed() -> true
-            else -> false
+            else -> {
+                removeSessionIfNeeded()
+                false
+            }
         }
     }
 
+    private fun removeSessionIfNeeded() {
+        val session = getSessionById() ?: return
+        if (session.source == Session.Source.ACTION_VIEW) requireComponents.core.sessionManager.remove(session)
+    }
+
     override fun onRequestPermissionsResult(
         requestCode: Int,
         permissions: Array<String>,