Not sure. Why not use this if not already using it ? https://www.mozilla.org/en-US/firefox/developer/

fyi: Suggest updating to prevent issues. Your Graphic Card Drivers are a year old as is the controller driver.

adapterDescription: Intel(R) HD Graphics 520

adapterDescription2: NVIDIA GeForce 920M

driverDate: 11-11-2016

driverDate2: 12-29-2016 driverVersion: 21.20.16.4550 driverVersion2: 21.21.13.7654

Please let us know if this solved your issue or if need further assistance.

There are little icons to collapse and show the left and right panels of the Debugger. The have a rough depiction of a narrow rectangle and a wide rectangle, with a triangle on the wide triangle. Can you find those buttons?

If the panel is so narrow that the button doesn't help, you may be able to reset the dimensions using the following method -- it works for windows and some dialogs, but I don't know about the Debugger.

Open your current Firefox settings (AKA Firefox profile) folder using either

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, click the "Open Folder" button. This should launch a new window listing various files and folders in Windows Explorer.

Leaving that window open, switch back to Firefox and Exit, either:

• "3-bar" menu button > "power" button
• (menu bar) File > Exit

Pause while Firefox finishes its cleanup, then rename xulstore.json to something like xulstore.old. If you see a file named localstore.rdf, rename that one to localstore.old.

Start Firefox back up again. Do the Debugger panels display normally again?

This process will hide the classic menu bar and Bookmarks Toolbar. To turn bars back on, you can use one of these methods to show the toolbar list and select the desired bars there:

• right-click (on Mac Ctrl+click) a blank spot on the tab bar (or the "+" button)
• (menu bar) View > Toolbars
  On Windows, tap the Alt key to activate the menu bar temporarily.
• in Customize mode > Show/Hide Toolbars (see: Customize Firefox controls, buttons and toolbars)

To turn on the Bookmarks Toolbar, Menu Bar, or other bars, click it on the list.

Thanks both.

I used device manager to attempt driver updates for the 520 and 920 devices but Windows 10 thinks they are up to date.

I renamed the xulstore.json file and restarted firefox. The "little icons to collapse and show the left and right panels of the Debugger" are not back

Some time ago I tried firefox developer and didn't like it. Can't remember why. I'll give it another try. The problem is that Chrome has gotten much better and their debugger is working very well for me. The actual bug I was trying to fix is long since fixed.

I'm going to save my settings and bookmarks, uninstall and reinstall firefox and see what that does.

In the meantime, the debugger is still dead.

Before doing anything else drastic, please check for any modified preferences:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste devt and pause while the list is filtered

Any modified preferences should be bolded and marked "modified" or "user set" -- anything that might affect the debugger that you could toggle back to its default value?

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance
• do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

I solved it by uninstalling firefox, reinstalling it and selecting the refresh firefox option.

Thanks for everyone's help.

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily. Thank you for contacting Mozilla Support.