Add new l10n string, but don't use it yet

public/locales/en-US/send.ftl

@@ -7,6 +7,8 @@ uploadPageExplainer = Send files through a safe, private, and encrypted link tha
 uploadPageLearnMore = Learn more
 uploadPageDropMessage = Drop your file here to start uploading
 uploadPageSizeMessage = For the most reliable operation, it’s best to keep your file under 1GB
+uploadPageBrowseButton = Select a file on your computer
+    .title = Select a file on your computer
 uploadPageBrowseButton1 = Select a file to upload
     .title = Select a file to upload
 uploadPageMultipleFilesAlert = Uploading multiple files or a folder is currently not supported.

views/index.handlebars

@@ -11,7 +11,7 @@
     <span id="file-size-msg"><em data-l10n-id="uploadPageSizeMessage"></em></span>
     <form method="post" action="upload" enctype="multipart/form-data">
       <label for="file-upload" id="browse"
-              data-l10n-id="uploadPageBrowseButton1"></label>
+              data-l10n-id="uploadPageBrowseButton"></label>
       <input id="file-upload" type="file" name="fileUploaded" />
     </form>
   </div>