diff --git a/src/lib/extension/BulkEntitiesTransporter.ts b/src/lib/extension/BulkEntitiesTransporter.ts
index 7594b25..b83fa49 100644
--- a/src/lib/extension/BulkEntitiesTransporter.ts
+++ b/src/lib/extension/BulkEntitiesTransporter.ts
@@ -1,7 +1,7 @@
 import type StorageEntity from "$lib/extension/base/StorageEntity";
 import { compressToEncodedURIComponent, decompressFromEncodedURIComponent } from "lz-string";
 import type { ImportableElementsList, ImportableEntityObject } from "$lib/extension/transporting/importables";
-import EntitiesTransporter from "$lib/extension/EntitiesTransporter";
+import EntitiesTransporter, { type SameSiteStatus } from "$lib/extension/EntitiesTransporter";
 import MaintenanceProfile from "$entities/MaintenanceProfile";
 import TagGroup from "$entities/TagGroup";
 
@@ -10,9 +10,17 @@ type TransportersMapping = {
 }
 
 export default class BulkEntitiesTransporter {
+  #lastSameSiteStatus: SameSiteStatus = null;
+
+  get lastImportSameSiteStatus() {
+    return this.#lastSameSiteStatus;
+  }
+
   parseAndImportFromJSON(jsonString: string): StorageEntity[] {
     let parsedObject: any;
 
+    this.#lastSameSiteStatus = null;
+
     try {
       parsedObject = JSON.parse(jsonString);
     } catch (e) {
@@ -23,7 +31,11 @@ export default class BulkEntitiesTransporter {
       throw new TypeError('Invalid or unsupported object!');
     }
 
-    return parsedObject.elements
+    this.#lastSameSiteStatus = EntitiesTransporter.checkIsSameSiteImportedObject(parsedObject);
+
+    let hasDifferentStatuses = false;
+
+    const resultEntities = parsedObject.elements
       .map(importableObject => {
         if (!(importableObject.$type in BulkEntitiesTransporter.#transporters)) {
           console.warn('Attempting to import unsupported entity: ' + importableObject.$type);
@@ -31,9 +43,21 @@ export default class BulkEntitiesTransporter {
         }
 
         const transporter = BulkEntitiesTransporter.#transporters[importableObject.$type as keyof App.EntityNamesMap];
-        return transporter.importFromObject(importableObject);
+        const resultEntity = transporter.importFromObject(importableObject);
+
+        if (transporter.lastImportSameSiteStatus !== this.#lastSameSiteStatus) {
+          hasDifferentStatuses = true;
+        }
+
+        return resultEntity;
       })
       .filter(maybeEntity => !!maybeEntity);
+
+    if (hasDifferentStatuses) {
+      this.#lastSameSiteStatus = 'unknown';
+    }
+
+    return resultEntities;
   }
 
   parseAndImportFromCompressedJSON(compressedJsonString: string): StorageEntity[] {
@@ -78,4 +102,19 @@ export default class BulkEntitiesTransporter {
     profiles: new EntitiesTransporter(MaintenanceProfile),
     groups: new EntitiesTransporter(TagGroup),
   }
+
+  /**
+   * Check if the imported object is created for the same site extension or not.
+   * @param importedObject Object to check.
+   * @private
+   */
+  static #checkIsSameSiteImportedObject(importedObject: Record<string, any>): SameSiteStatus {
+    if (!('$site' in importedObject)) {
+      return "unknown";
+    }
+
+    return importedObject.$site === __CURRENT_SITE__
+      ? "same"
+      : "different";
+  }
 }
diff --git a/src/lib/extension/EntitiesTransporter.ts b/src/lib/extension/EntitiesTransporter.ts
index ac29569..0b90cec 100644
--- a/src/lib/extension/EntitiesTransporter.ts
+++ b/src/lib/extension/EntitiesTransporter.ts
@@ -2,10 +2,33 @@ import { validateImportedEntity } from "$lib/extension/transporting/validators";
 import { exportEntityToObject } from "$lib/extension/transporting/exporters";
 import StorageEntity from "$lib/extension/base/StorageEntity";
 import { compressToEncodedURIComponent, decompressFromEncodedURIComponent } from "lz-string";
+import type { ImportableElement } from "$lib/extension/transporting/importables";
+
+/**
+ * Status of the last import.
+ *
+ * - `NULL` - no import was done yet or was unsuccessful.
+ * - `"unknown"` — imported object was created before v0.5, when extension started to be built for multiple sites.
+ * - `"same"` — imported object is marked as generated by the same type of extension.
+ * - `"different"` — imported object is marked as generated by some other type of extension.
+ */
+export type SameSiteStatus = null | "unknown" | "same" | "different";
 
 export default class EntitiesTransporter<EntityType> {
   readonly #targetEntityConstructor: new (...any: any[]) => EntityType;
 
+  #lastSameSiteStatus: SameSiteStatus = null;
+
+  /**
+   * Read the status of the last successful import. This flag could be used to determine if it was for the same site as
+   * the current extension or when it's generated before site identity was passed to the importable object.
+   *
+   * @see {SameSiteStatus} For the list of possible statuses.
+   */
+  get lastImportSameSiteStatus() {
+    return this.#lastSameSiteStatus;
+  }
+
   /**
    * Name of the entity, exported directly from the constructor.
    * @private
@@ -37,6 +60,8 @@ export default class EntitiesTransporter<EntityType> {
   }
 
   importFromObject(importedObject: Record<string, any>): EntityType {
+    this.#lastSameSiteStatus = null;
+
     // TODO: There should be an auto-upgrader somewhere before the validation. So if even the older version of schema
     //       was used, we still will will be able to pass the validation. For now we only have non-breaking changes.
     validateImportedEntity(
@@ -44,6 +69,8 @@ export default class EntitiesTransporter<EntityType> {
       importedObject,
     );
 
+    this.#lastSameSiteStatus = EntitiesTransporter.checkIsSameSiteImportedObject(importedObject);
+
     return new this.#targetEntityConstructor(
       importedObject.id,
       importedObject
@@ -54,6 +81,7 @@ export default class EntitiesTransporter<EntityType> {
     const importedObject = this.#tryParsingAsJSON(jsonString);
 
     if (!importedObject) {
+      this.#lastSameSiteStatus = null;
       throw new Error('Invalid JSON!');
     }
 
@@ -108,4 +136,18 @@ export default class EntitiesTransporter<EntityType> {
 
     return jsonObject
   }
+
+  /**
+   * Check if the imported object is created for the same site extension or not.
+   * @param importedObject Object to check.
+   */
+  static checkIsSameSiteImportedObject(importedObject: Record<string, any>): SameSiteStatus {
+    if (!('$site' in importedObject)) {
+      return "unknown";
+    }
+
+    return importedObject.$site === __CURRENT_SITE__
+      ? "same"
+      : "different";
+  }
 }