diff --git a/js/tb115_segmenter/tb115_loader.js b/js/tb115_segmenter/tb115_loader.js
new file mode 100644
index 00000000..f5bbf28d
--- /dev/null
+++ b/js/tb115_segmenter/tb115_loader.js
@@ -0,0 +1,65 @@
+/*
+ *  ThunderAI [https://micz.it/thunderbird-addon-thunderai/]
+ *  Copyright (C) 2024  Mic (m@micz.it)
+
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+// Firefox 115 and, consequently, Thunderbird 115 are not compatible with Intl.Segmenter.
+// ChatGPT is using Intl.Segmenter, so we have to do something about it or it won't work...
+
+console.log("[ThunderAI] Intl.Segmenter: " + Intl.Segmenter);
+
+(function() {
+    if('Segmenter' in Intl){
+        console.log('[ThunderAI] TB128+ detected. Intl.Segmenter is already supported.');
+        return;
+    }
+    // Creates a <script> element to inject polyfill.js into the page context
+    const script = document.createElement('script');
+    script.src = browser.runtime.getURL('js/tb115_segmenter/tb115_polyfill.js');
+    script.onload = function() {
+        // Remove the script once loaded for cleanup
+        this.remove();
+    };
+    script.onerror = function() {
+        console.error('[ThunderAI] Error loading Intl.Segmenter polyfill.');
+    };
+    (document.head || document.documentElement).appendChild(script);
+})();
+
+
+
+async function isThunderbird128OrGreater(){
+    try {
+      const info = await browser.runtime.getBrowserInfo();
+      const version = info.version;
+      return compareThunderbirdVersions(version, '128.0') >= 0;
+    } catch (error) {
+      console.error('[ThunderAI] Error retrieving browser information:', error);
+      return false;
+    }
+  }
+  
+  function compareThunderbirdVersions(v1, v2) {
+    const v1parts = v1.split('.').map(Number);
+    const v2parts = v2.split('.').map(Number);
+  
+    for (let i = 0; i < Math.max(v1parts.length, v2parts.length); i++) {
+      const v1part = v1parts[i] || 0;
+      const v2part = v2parts[i] || 0;
+      if (v1part > v2part) return 1;
+      if (v1part < v2part) return -1;
+    }
+    return 0;
+  }
\ No newline at end of file
diff --git a/js/tb115_segmenter/tb115_polyfill.js b/js/tb115_segmenter/tb115_polyfill.js
new file mode 100644
index 00000000..597ddd4d
--- /dev/null
+++ b/js/tb115_segmenter/tb115_polyfill.js
@@ -0,0 +1,48 @@
+/*
+ *  ThunderAI [https://micz.it/thunderbird-addon-thunderai/]
+ *  Copyright (C) 2024  Mic (m@micz.it)
+
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+// Firefox 115 and, consequently, Thunderbird 115 are not compatible with Intl.Segmenter.
+// ChatGPT is using Intl.Segmenter, so we have to do something about it or it won't work...
+
+(function() {
+    if (!('Segmenter' in Intl)) {
+        class Segmenter {
+            constructor(locale = 'en', options = { granularity: 'grapheme' }) {
+                this.locale = locale;
+                this.granularity = options.granularity || 'grapheme';
+            }
+
+            segment(text) {
+                switch (this.granularity) {
+                    case 'word':
+                        return text.split(/\s+/).filter(word => word.length > 0).map(word => ({ segment: word }));
+                    case 'grapheme':
+                        return Array.from(text).map(char => ({ segment: char }));
+                    case 'sentence':
+                        return text.split(/(?<=[.!?])\s+/).map(sentence => ({ segment: sentence }));
+                    default:
+                        return [{ segment: text }];
+                }
+            }
+        }
+
+        Intl.Segmenter = Segmenter;
+        console.log('Intl.Segmenter polyfill correctly loaded.');
+    } else {
+        console.log('Intl.Segmenter is already supported.');
+    }
+})();
diff --git a/manifest.json b/manifest.json
index 13f40295..feb56b34 100644
--- a/manifest.json
+++ b/manifest.json
@@ -49,5 +49,13 @@
         "_thunderai__do_action": {
         "description": "Opens the ThunderAI prompts menu"
         }
-    }
+    },
+    "content_scripts": [
+        {
+            "matches": ["https://*.chatgpt.com/*"],
+            "js": ["js/tb115_segmenter/tb115_loader.js"],
+            "all_frames": true,
+            "run_at": "document_start"
+        }
+    ]
 }