diff --git a/www/index.html b/www/index.html
index bd496337..5fcda888 100644
--- a/www/index.html
+++ b/www/index.html
@@ -1086,6 +1086,13 @@
                                         <span class="checkmark"></span>
                                         <b>Permanently hide active content warning</b> (for experienced users)
                                     </label>
+                                    <b>Force use of libzim W/ASM for reading full-text index:</b>
+                                    <select name="debugLibzimASM" id="debugLibzimASMDrop">
+                                        <option value="">Default</option>
+                                        <option value="wasm">WASM</option>
+                                        <option value="asm">ASM</option>
+                                    </select>
+                                    <p><i>Warning! Disables OS checks and may stop app from working!</i></p>
                                     <label id="bypassAppCacheDiv" class="checkbox" title="WARNING: Leaving this checked will prevent offline usage of the PWA. Setting will clear all existing Cache API caches, but assetsCache will be used unless also disabled above. For testing new code with the PWA.">
                                         <input type="checkbox" name="bypassAppCache" id="bypassAppCacheCheck">
                                         <span class="checkmark"></span>
diff --git a/www/js/app.js b/www/js/app.js
index 7b71159a..89833cde 100644
--- a/www/js/app.js
+++ b/www/js/app.js
@@ -1329,6 +1329,10 @@ define(['jquery', 'zimArchiveLoader', 'uiUtil', 'util', 'utf8', 'cache', 'images
             params.hideActiveContentWarning = this.checked ? true : false;
             settingsStore.setItem('hideActiveContentWarning', params.hideActiveContentWarning, Infinity);
         });
+        document.getElementById('debugLibzimASMDrop').addEventListener('change', function (event) {
+            params.debugLibzimASM = event.target.value || false;
+            settingsStore.setItem('debugLibzimASM', params.debugLibzimASM, Infinity);
+        })
         $('input:checkbox[name=openExternalLinksInNewTabs]').on('change', function () {
             params.openExternalLinksInNewTabs = this.checked ? true : false;
             settingsStore.setItem('openExternalLinksInNewTabs', params.openExternalLinksInNewTabs, Infinity);
@@ -3382,6 +3386,11 @@ define(['jquery', 'zimArchiveLoader', 'uiUtil', 'util', 'utf8', 'cache', 'images
                                     });
                                 }
                             }
+                            if (!selectedFileSet.length) {
+                                reject('The requested archive is not in the archive folder ' + folder + '!');
+                            }
+                        } else {
+                            reject('The requested archive does not appear to be a ZIM file!');
                         }
                     } else {
                         // Folder was empty...
diff --git a/www/js/init.js b/www/js/init.js
index e5715fab..44ff93fa 100644
--- a/www/js/init.js
+++ b/www/js/init.js
@@ -129,7 +129,7 @@ params.pagesLoaded = 0; // Page counter used to show PWA Install Prompt only aft
 params.localUWPSettings = /UWP/.test(params.appType) ? Windows.Storage.ApplicationData.current.localSettings.values : null;
 appstate['target'] = 'iframe'; // The target for article loads (this should always be 'iframe' initially, and will only be changed as a result of user action)
 params['mapsURI'] = getSetting('mapsURI') || (/UWP|Windows/.test(params.appType) ? 'bingmaps:' : 'https://www.openstreetmap.org/'); // Protocol with colon ('bingmaps:') or URL with final slash ('https://www.openstreetmap.org/')
-params['debugLibzimASM'] = null; // 'wasm|asm' Forces use of wasm or asm for libzim decoder. You can also set this as an override URL querystring e.g. ?debugLibzimASM=wasm;
+params['debugLibzimASM'] = getSetting('degugLibzimASM'); // 'wasm|asm' Forces use of wasm or asm for libzim decoder. You can also set this as an override URL querystring e.g. ?debugLibzimASM=wasm;
 
 // Apply any override parameters in querystring (done as a self-calling function to avoid creating global variables)
 (function overrideParams() {
@@ -246,6 +246,7 @@ document.getElementById('hideToolbarsCheck').indeterminate = params.hideToolbars
 document.getElementById('hideToolbarsCheck').readOnly = params.hideToolbars === "top";
 document.getElementById('hideToolbarsState').innerHTML = (params.hideToolbars === "top" ? "top" : params.hideToolbars ? "both" : "never");
 document.getElementById('openExternalLinksInNewTabsCheck').checked = params.openExternalLinksInNewTabs;
+document.getElementById('debugLibzimASMDrop').value = params.debugLibzimASM || '';
 if (params.windowOpener === null) { // Setting has never been activated, so determine a sensible default
     params.windowOpener = /UWP/.test(params.appType) && params.contentInjectionMode === 'jquery' ? false : 
     'MSBlobBuilder' in window ? 'window' : // IE11/Edge/UWP work best in window mode, not in tab mode!