diff --git a/platform/firefox/frameModule.js b/platform/firefox/frameModule.js
index ad24e495f..8288fcfab 100644
--- a/platform/firefox/frameModule.js
+++ b/platform/firefox/frameModule.js
@@ -153,13 +153,24 @@ const contentObserver = {
         // so check context.top instead of context
         if ( context.top && context.location ) {
             // https://bugzil.la/1092216
-            getMessageManager(context).sendRpcMessage(this.cpMessageName, {
+            let messageManager = getMessageManager(context);
+            let details = {
                 openerURL: openerURL || null,
                 url: location.spec,
                 type: type,
                 frameId: type === this.MAIN_FRAME ? -1 : (context === context.top ? 0 : 1),
                 parentFrameId: context === context.top ? -1 : 0
-            });
+            };
+
+            // TODO: frameId from outerWindowID?
+            // https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/Reference/Interface/nsIDOMWindowUtils
+
+            if ( typeof messageManager.sendRpcMessage === 'function' ) {
+                messageManager.sendRpcMessage(this.cpMessageName, details);
+            } else {
+                // Compatibility for older versions
+                messageManager.sendSyncMessage(this.cpMessageName, details);
+            }
         }
 
         return this.ACCEPT;
diff --git a/platform/firefox/install.rdf b/platform/firefox/install.rdf
index 9cbbd7f58..c1534e143 100644
--- a/platform/firefox/install.rdf
+++ b/platform/firefox/install.rdf
@@ -17,7 +17,7 @@
         <targetApplication>
             <r:Description>
                 <id>{{ec8030f7-c20a-464f-9b0e-13a3a9e97384}}</id>
-                <minVersion>29.0</minVersion>
+                <minVersion>24.0</minVersion>
                 <maxVersion>38.0</maxVersion>
             </r:Description>
         </targetApplication>
@@ -26,7 +26,7 @@
         <targetApplication>
             <r:Description>
                 <id>{{92650c4d-4b8e-4d2a-b7eb-24ecf4f6b63a}}</id>
-                <minVersion>2.26</minVersion>
+                <minVersion>2.21</minVersion>
                 <maxVersion>2.35</maxVersion>
             </r:Description>
         </targetApplication>
diff --git a/platform/firefox/vapi-background.js b/platform/firefox/vapi-background.js
index ae799b06b..994aa7f0a 100644
--- a/platform/firefox/vapi-background.js
+++ b/platform/firefox/vapi-background.js
@@ -45,7 +45,7 @@ vAPI.firefox = true;
 // TODO: read these data from somewhere...
 vAPI.app = {
     name: 'µBlock',
-    version: '0.8.5.3'
+    version: '0.8.5.4'
 };
 
 /******************************************************************************/
@@ -366,7 +366,7 @@ vAPI.tabs.registerListeners = function() {
 
 vAPI.tabs.getTabId = function(target) {
     if ( target.linkedPanel ) {
-        return target.linkedPanel.slice(6);
+        return target.linkedPanel;
     }
 
     var i, gBrowser = target.ownerDocument.defaultView.gBrowser;
@@ -374,13 +374,13 @@ vAPI.tabs.getTabId = function(target) {
     // This should be more efficient from version 35
     if ( gBrowser.getTabForBrowser ) {
         i = gBrowser.getTabForBrowser(target);
-        return i ? i.linkedPanel.slice(6) : -1;
+        return i ? i.linkedPanel : -1;
     }
 
     i = gBrowser.browsers.indexOf(target);
 
     if ( i !== -1 ) {
-        i = gBrowser.tabs[i].linkedPanel.slice(6);
+        i = gBrowser.tabs[i].linkedPanel;
     }
 
     return i;
@@ -399,7 +399,7 @@ vAPI.tabs.get = function(tabId, callback) {
 
         for ( var win of windows ) {
             tab = win.gBrowser.tabContainer.querySelector(
-                'tab[linkedpanel="panel-' + tabId + '"]'
+                'tab[linkedpanel="' + tabId + '"]'
             );
 
             if ( tab ) {
@@ -541,7 +541,7 @@ vAPI.tabs.remove = function(tabIds) {
     }
 
     tabIds = tabIds.map(function(tabId) {
-        return 'tab[linkedpanel="panel-' + tabId + '"]';
+        return 'tab[linkedpanel="' + tabId + '"]';
     }).join(',');
 
     for ( var win of this.getWindows() ) {
@@ -580,6 +580,7 @@ vAPI.tabs.injectScript = function(tabId, details, callback) {
         details.file = vAPI.getURL(details.file);
     }
 
+
     tab.linkedBrowser.messageManager.sendAsyncMessage(
         location.host + ':broadcast',
         JSON.stringify({
@@ -1135,7 +1136,12 @@ vAPI.toolbarButton = {
 /******************************************************************************/
 
 vAPI.toolbarButton.init = function() {
-    var {CustomizableUI} = Cu.import('resource:///modules/CustomizableUI.jsm', null);
+    try {
+        var {CustomizableUI} = Cu.import('resource:///modules/CustomizableUI.jsm', null);
+    } catch (ex) {
+        return;
+    }
+
     this.defaultArea = CustomizableUI.AREA_NAVBAR;
     this.styleURI = [
         '#' + this.id + ' {',
diff --git a/src/css/dashboard.css b/src/css/dashboard.css
index 12065ea94..329e41287 100644
--- a/src/css/dashboard.css
+++ b/src/css/dashboard.css
@@ -65,4 +65,5 @@ iframe {
     height: 100%;
     border-top: 50px solid transparent;
     box-sizing: border-box;
+    -moz-box-sizing: border-box;
     }
diff --git a/src/css/devtool-log.css b/src/css/devtool-log.css
index 1ae60b44e..1d7fb3440 100644
--- a/src/css/devtool-log.css
+++ b/src/css/devtool-log.css
@@ -1,6 +1,7 @@
 body {
     border: 0;
     box-sizing: border-box;
+    -moz-box-sizing: border-box;
     font: 12px monospace;
     margin: 0;
     overflow-x: hidden;
diff --git a/src/css/devtools.css b/src/css/devtools.css
index f3022e730..4f29fb19f 100644
--- a/src/css/devtools.css
+++ b/src/css/devtools.css
@@ -8,6 +8,7 @@ body {
     background-color: #eee;
     border: none;
     box-sizing: border-box;
+    -moz-box-sizing: border-box;
     height: 4em;
     padding: 1em;
     position: fixed;
@@ -41,6 +42,7 @@ select option {
 #content {
     border: 0;
     box-sizing: border-box;
+    -moz-box-sizing: border-box;
     height: calc(100vh - 4em);
     margin-top: 4em;
     overflow-y: auto;
diff --git a/src/css/popup.css b/src/css/popup.css
index 5edd1b5b2..0a3a6016d 100644
--- a/src/css/popup.css
+++ b/src/css/popup.css
@@ -192,6 +192,7 @@ body.dirty #refresh:hover {
     background-color: transparent;
     border: none;
     box-sizing: border-box;
+    -moz-box-sizing: border-box;
     color: #000;
     display: inline-block;
     height: 24px;