[Editor] Load the model when the user switch to the stamp editing mode

web/firefoxcom.js

@@ -329,10 +329,6 @@ class MLManager {
     this.altTextLearnMoreUrl = altTextLearnMoreUrl;
     this.enableAltTextModelDownload = enableAltTextModelDownload;
     this.enableGuessAltText = enableGuessAltText;
-
-    if (enableAltTextModelDownload) {
-      this.#loadAltTextEngine(false);
-    }
   }
 
   async isEnabledFor(name) {
@@ -356,6 +352,12 @@ class MLManager {
     ]);
   }
 
+  async loadModel(name) {
+    if (name === "altText" && this.enableAltTextModelDownload) {
+      await this.#loadAltTextEngine(false);
+    }
+  }
+
   async downloadModel(name) {
     if (name !== "altText") {
       return null;

web/genericcom.js

@@ -88,6 +88,8 @@ class FakeMLManager {
     return null;
   }
 
+  async loadModel(_name) {}
+
   async downloadModel(_name) {
     // Simulate downloading the model but with progress.
     // The progress can be seen in the new alt-text dialog.

web/pdf_viewer.js

@@ -906,6 +906,9 @@ class PDFViewer {
               uiManager: this.#annotationEditorUIManager,
             });
             if (mode !== AnnotationEditorType.NONE) {
+              if (mode === AnnotationEditorType.STAMP) {
+                this.#mlManager?.loadModel("altText");
+              }
               this.#annotationEditorUIManager.updateMode(mode);
             }
           } else {
@@ -2311,6 +2314,9 @@ class PDFViewer {
     if (!this.pdfDocument) {
       return;
     }
+    if (mode === AnnotationEditorType.STAMP) {
+      this.#mlManager?.loadModel("altText");
+    }
 
     const { eventBus } = this;
     const updater = () => {