Read these two articles, do they or the linked information help ?

• unable to download or save files
• Warning unresponsive script

So far, so good. Seems to have stopped now. How did I do this? I cleared the downloads list box which probably had hundreds of downloads listed. I will keep an eye on it but I have just completed 10 downloads without a freeze. Thanks, Leslie

Glad the problem was solved.

That is this part of the code in chrome://mozapps/content/downloads/downloads.js (paste in the location bar)

  // Add another item to the list if we should; otherwise, let the UI update
  // and continue later
  if (aNumItems > 1) {
    stepListBuilder(aNumItems - 1);
  }

I do not understand what you are saying

It is not that important.

It identifies which code your error message is referring to (line 1222 in the file downloads.js) in case others ant to check it. That file is part of Firefox (located in omni.jar) and you can inspect such files by pasting or typing the URL in the location bar.

I have had this same problem for a couple of months. It doesn't happen all the time but seems to happen the first time I download something after rebooting.

I downloaded download.js and What I see at line 1222 is:

     // Because of the joys of XBL, we can't update the buttons until the
     // download object is in the document.
     updateButtons(item);

Am I getting a newer version or something?

The complete code that decides to call updateButtons is this:

   // Make the item and add it to the end if it's active or matches the search
   let item = createDownloadItem(attrs);
   if (item && (isActive || downloadMatchesSearch(item))) {
     // Add item to the end
     gDownloadsView.appendChild(item);
   
     // Because of the joys of XBL, we can't update the buttons until the
     // download object is in the document.
     updateButtons(item);
   } else {
     // We didn't add an item, so bump up the number of items to process, but
     // not a whole number so that we eventually do pause for a chunk break
     aNumItems += .9;
   }
 } catch (e) {
   // Something went wrong when stepping or getting values, so clear and quit
   gStmt.reset();
   return;
 }

So it seems to be getting stuck when adding the new download to the list of downloads. I cleared my download history so I will see if that fixes it and post here if it did.