diff --git a/src/background.ts b/src/background.ts
index b0af7de..2db72b9 100644
--- a/src/background.ts
+++ b/src/background.ts
@@ -93,7 +93,7 @@
           chrome.windows.create({type: 'popup', url, width: 1000, height: 382});
         } else {
           chrome.tabs.create(newTabOptions, tab => {
-            ExtSessionStorage.set({translatorTab: tab.id});
+            ExtSessionStorage.set({translatorTab: tab?.id});
           });
         }
       })
diff --git a/src/common/sessionStorage_mv2.ts b/src/common/sessionStorage_mv2.ts
index dda0ae1..55990f3 100644
--- a/src/common/sessionStorage_mv2.ts
+++ b/src/common/sessionStorage_mv2.ts
@@ -1,47 +1,50 @@
-declare global {
-  interface Window {
-    extCustomStorage: any;
-  }
-}
+// WARNING: In MV2, data is persisted even after the session ends,[1] unlike
+// with chrome.storage.session in MV3.
+//
+// Before, this class in MV2 only persisted data until the background page was
+// unloaded, so this introduced bug
+// https://iavm.xyz/b/translateselectedtext/18.
+//
+// Thus, since making the background page persistent will impact performance,
+// the easiest solution is to let this custom session storage be persistent in
+// MV2, because persistence of this storage won't affect the extension, and
+// although this solution isn't nice and could introduce some smaller bugs, MV2
+// will be deprecated soon anyways.
+//
+// [1]: The only exception is the translatorTab value, which will be erased when
+// the corresponding tab is closed. This is because after a browser restart,
+// already used tab IDs can be reused again, so we could end up opening Google
+// Translate in an unrelated tab otherwise.
+//
+// Also, we'll delete this value when starting the browser as another
+// "protection layer", since closing the browser sometimes results in the
+// onRemoved event not being handled.
+//
+// Keep in mind there are some edge cases where we could still be reusing an
+// unrelated tab. A known one is when the extension is disabled for some period
+// of time and afterwards enabled again, but there might be others.
+
+chrome.runtime.onStartup.addListener(() => {
+  chrome.storage.local.remove('translatorTab');
+});
+
+chrome.tabs.onRemoved.addListener(tabId => {
+  ExtSessionStorage.get('translatorTab').then(items => {
+    if (tabId === items['translatorTab'])
+      chrome.storage.local.remove('translatorTab');
+  });
+});
 
 export default class ExtSessionStorage {
   static set(items: any): Promise<void> {
-    return new Promise((res, rej) => {
-      if (window.extCustomStorage === undefined) window.extCustomStorage = {};
-
-      for (const [key, value] of Object.entries(items))
-        window.extCustomStorage[key] = value;
-
-      res();
-    });
+    return chrome.storage.local.set(items);
   }
 
   static get(keys: string|Array<string>|undefined): Promise<any> {
-    return new Promise((res, rej) => {
-      if (window.extCustomStorage === undefined) window.extCustomStorage = {};
-
-      if (keys === undefined) {
-        res(window.extCustomStorage);
-        return;
-      }
-
-      if (typeof keys === 'string') {
-        const key = keys;
-        keys = [key];
-      }
-
-      if (Array.isArray(keys)) {
-        let returnObject: any = {};
-        for (const key of keys) {
-          returnObject[key] = window.extCustomStorage[key];
-        }
-        res(returnObject);
-        return;
-      }
-
-      rej(new Error(
-          'The keys passed are not a valid type ' +
-          '(undefined, string or array).'));
+    return new Promise((res, _) => {
+      chrome.storage.local.get(keys, items => {
+        res(items);
+      });
     });
   }
 }