diff --git a/l10n/en-US/viewer.ftl b/l10n/en-US/viewer.ftl
index be2ddedc4a0b0..3c3bed572b394 100644
--- a/l10n/en-US/viewer.ftl
+++ b/l10n/en-US/viewer.ftl
@@ -447,9 +447,6 @@ pdfjs-editor-new-alt-text-error-close-button = Close
 #   $downloadedSize (Number) - the downloaded size (in MB) of the AI model.
 #   $percent (Number) - the percentage of the downloaded size.
 pdfjs-editor-new-alt-text-ai-model-downloading-progress = Downloading alt text AI model ({ $downloadedSize } of { $totalSize } MB)
-    .aria-valuemin = 0
-    .aria-valuemax = { $totalSize }
-    .aria-valuenow = { $downloadedSize }
     .aria-valuetext = Downloading alt text AI model ({ $downloadedSize } of { $totalSize } MB)
 
 # This is a button that users can click to edit the alt text they have already added.
diff --git a/web/new_alt_text_manager.js b/web/new_alt_text_manager.js
index 4a5012419f868..1ab2067aa251c 100644
--- a/web/new_alt_text_manager.js
+++ b/web/new_alt_text_manager.js
@@ -299,9 +299,13 @@ class NewAltTextManager {
       totalLoaded = Math.min(0.99 * total, totalLoaded);
 
       // Update the progress.
+      const totalSize = (this.#downloadModelDescription.ariaValueMax =
+        Math.round(total / ONE_MEGA_BYTES));
+      const downloadedSize = (this.#downloadModelDescription.ariaValueNow =
+        Math.round(totalLoaded / ONE_MEGA_BYTES));
       this.#downloadModelDescription.setAttribute(
         "data-l10n-args",
-        `{"totalSize": ${Math.round(total / ONE_MEGA_BYTES)}, "downloadedSize": ${Math.round(totalLoaded / ONE_MEGA_BYTES)}}`
+        JSON.stringify({ totalSize, downloadedSize })
       );
       if (!finished) {
         return;
diff --git a/web/viewer.html b/web/viewer.html
index 3bcd43e0b0909..e9162220358f4 100644
--- a/web/viewer.html
+++ b/web/viewer.html
@@ -576,7 +576,7 @@
                   <label for="newAltTextCreateAutomaticallyButton" class="togglerLabel" data-l10n-id="pdfjs-editor-new-alt-text-create-automatically-button-label">Create alt text automatically</label>
                 </div>
                 <div id="newAltTextDownloadModel" class="hidden">
-                  <span id="newAltTextDownloadModelDescription" data-l10n-id="pdfjs-editor-new-alt-text-ai-model-downloading-progress" data-l10n-args='{ "totalSize": 0, "downloadedSize": 0 }'>Downloading alt text AI model (0 of 0 MB)</span>
+                  <span id="newAltTextDownloadModelDescription" data-l10n-id="pdfjs-editor-new-alt-text-ai-model-downloading-progress" aria-valuemin="0" data-l10n-args='{ "totalSize": 0, "downloadedSize": 0 }'>Downloading alt text AI model (0 of 0 MB)</span>
                 </div>
               </div>
               <div id="newAltTextImagePreview"></div>