I had the very same problems on Sandboxes.
I have opened Salesforce ticket and they referred me again to this SSE post.
And also to a similar SSE post.
Jermaine's answer to that post helped for me.
If I copy the URL for the developer console into a new window, it opened in the new window without issue. After that I was able to open it directly as popup window from Salesforce.
Later Salesforce support shared this knowledge article with me.
I believe this should always help.
Knowledge Article Number: 000205278
Description: When I'm trying to open the Developer Console it freezes the browser and, depending on the browser, we can see the following error:
"A script on this page may be busy, or it may have stopped responding. You can stop the script now, open the script in the debugger, or let the script continue."
Resolution: The solution would be to reset the IDEWorkspace for the affected user. To do this, please:
- Open the Developer Console as the affected user.
- When the error appears, please the "Debug Script" button. If you don't have a "Debug Script" button you'll have to open the Browser's Developer Tools manually (please scroll down to the bottom of this Article for additional information).
- Move to the 'Network" tab of the browser's Dev Tools.
- You'll find a number of requests, if you don't, please refresh the browser. We're interested in a request with the following format:
- The 'Id' value is the one we are looking for. Please copy that.
- Open Workbench. Select "Utilities" and then "REST Explorer".
- Do a GET request for "/services/data/v29.0/tooling/sobjects/IDEWorkspace/1deQ00000004HmJIAU" - remember to replace the "1deQ00000004HmJIAU" parameter with the "Id" relevant to your org that you obtained in step #5.
- You will see the content of the affected user's IDEWorkspace.
- Do a DELETE request.
- Re-open Developer Console
After following these steps the Menus should be available again and the error message should no longer appear.
The entire Developer Console is built in JavaScript, which, despite recent advances in software and hardware, remains relatively slow in many cases compared to native applications. One place you'll notice this problem is in cases where a ton of work has to be done in a short period of time. Try setting your debug logs to the maximum setting, then try using the full perspective (Debug > Switch Perspective).
If you are debugging a log near 2MB, your browser will probably freeze momentarily trying to render the log. It's really not designed to do that, but we developers try anyways. Also, while in a maximum perspective, change the size of your window, and observe how it appears to stutter or freeze on the inside.
Now, to get to my point, when you're running a batch with say, 10,000 batches, the log table has to be redrawn many times per second potentially, with rapidly increasing memory usage and tons of elements. Your browser will try to accommodate the request to constantly redraw, eventually slowing to a crawl. You'll find that not only the Developer Console unresponsive, but the page you launched the Developer Console will also act jittery and/or freeze. This is because of JavaScript's single-thread model.
Run batches as an alternate user, when possible, or keep such batches small. Clear your logs frequently, as well, since once you get to a couple of hundred logs, you'll notice a pretty sharp decline in performance. You'll probably eventually need to close the window every so often and/or all of the files you're working on, or the console will eventually become slow as things keep piling on, such as the progress sub-tab, which can accumulate thousands of items of its own.
Best Answer
I ran into the same issue. I took a shot in the dark and copied the URL for the developer console into a new window. It opened in the new window without issue. I was then able to open it directly through Sales force. Hope this works for you.