v2.5.0 work on Firefox for Android.

content_scripts/content.js

@@ -18,8 +18,32 @@ let domTextarea = null;
 domMenuitem.addEventListener('click', function(){
     document.body.appendChild(domTextarea);
     domTextarea.select();
-    document.execCommand('copy');
-    domTextarea.remove();
+    let bln = document.execCommand('copy');
+    if(bln){
+      domTextarea.remove();
+    }else{
+      let scrollX = window.screenX;
+      let scrollY = window.scrollY;
+
+      // https://bugzilla.mozilla.org/show_bug.cgi?id=1420466
+      let newtext = document.createTextNode('Copying text command was successful. Click to continue.');
+      let domDiv = document.createElement('div');
+      domDiv.style.backgroundColor = 'white';
+      domDiv.style.width = '80%';
+      domDiv.style.margin = '0 auto';
+      domDiv.style.padding = 10;
+      domDiv.appendChild(newtext);
+      let myLightbox = lightbox({
+        contentNode: domDiv
+      });
+      myLightbox.addEventListener('click', function(){
+        domTextarea.select();
+        document.execCommand('copy');
+        domTextarea.remove();
+        myLightbox.remove();
+        window.scroll(scrollX, scrollY);
+      });
+    }
 });
 
 domMenu.appendChild(domMenuitem);

content_scripts/lightbox.js

@@ -0,0 +1,29 @@
+'use strict';
+let lightbox = function(objOption){
+	let domDiv = document.createElement('div');
+	domDiv.setAttribute('style', 'position:fixed;top:0;left:0;width:100%;height:100%;background:rgba(0, 0, 0, .8);');
+	domDiv.style.display = 'none';
+	domDiv.addEventListener('click', function(){
+		domDiv.style.display = 'none';
+	});
+	let domTable = document.createElement('table');
+	let domTr = document.createElement('tr');
+	let domTd = document.createElement('td');
+	domTable.setAttribute('style', 'width:100%;height:100%;');
+	domTd.setAttribute('style', 'vertical-align:middle; text-align:center;');
+
+	domTd.appendChild(objOption.contentNode);
+	domTr.appendChild(domTd);
+	domTable.appendChild(domTr);
+	domDiv.appendChild(domTable);
+	document.body.appendChild(domDiv);
+	if(objOption.opener){
+		objOption.opener.addEventListener('click', function(){
+			domDiv.style.display = 'inline';
+		});
+	}else{
+		domDiv.style.display = 'inline';
+	}
+
+	return domDiv;
+};

manifest.json

@@ -2,7 +2,7 @@
   "name": "Fennec Copy Link Text",
   "description": "This addon adds a menu item to the context menu, and it lets you easily copy the visible text of the selected link.",
   "manifest_version": 2,
-  "version": "2.0.0",
+  "version": "2.5.0",
   "homepage_url": "https://github.com/shyangs/Fennec-Copy-Link-Text",
 
   "applications": {
@@ -22,7 +22,10 @@
 
   "content_scripts": [{
     "matches": ["<all_urls>", "file:///*"],
-    "js": ["content_scripts/content.js"],
+    "js": [
+      "content_scripts/lightbox.js",
+      "content_scripts/content.js"
+    ],
     "run_at": "document_end",
     "all_frames": true
   }]