Did you try the Firefox SafeMode vs Windows Safe Mode?

Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• Click the menu button , click Help and select Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

If that doesn't work, I am at loss as to what to suggest.

After the above,

Start your Computer in safe mode with networking. Then start Firefox. Try Safe web sites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Type about:support in the address bar and press Enter. Under the main banner, press the button; Copy Text To Clipboard.. Then in the reply box at the bottom of this page, do a right click in the box and select Paste. This will show us your system details. No Personal Information Is Collected.

Tried all the above. Firefox in safe mode. Windows in safe mode - firefox normal. Windows in safe mode - firefox in safe mode. Nothing. about:customizing brings up a blank page. Right clicking the toolbar and choosing customize takes no action.

Here's the support information from my computer: Application Basics

Name: Firefox Version: 42.0 Build ID: 20151029151421 Update Channel: release User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:42.0) Gecko/20100101 Firefox/42.0 Multiprocess Windows: 0/1 (default: false) Safe Mode: false

Crash Reports for the Last 3 Days

All Crash Reports

Extensions

Name: Dashlane Version: 3.5.2.94798 Enabled: true ID: jetpack-extension@dashlane.com

Name: Troubleshooter Version: 1.1a.1-signed Enabled: true ID: troubleshooter@mozilla.org

Graphics

Adapter Description: Microsoft Basic Display Driver Adapter Drivers: Unknown Adapter RAM: Unknown Asynchronous Pan/Zoom: none Device ID: 0x00ba Direct2D Enabled: Blocked for your graphics card because of unresolved driver issues. DirectWrite Enabled: false (10.0.10240.16430) Driver Date: 6-21-2006 Driver Version: 10.0.10240.16384 GPU #2 Active: false GPU Accelerated Windows: 1/1 Direct3D 11 WARP (OMTC) Subsys ID: 000000ba Supports Hardware H264 Decoding: false Vendor ID: 0x00ba WebGL Renderer: Blocked for your graphics card because of unresolved driver issues. windowLayerManagerRemote: true AzureCanvasBackend: skia AzureContentBackend: cairo AzureFallbackCanvasBackend: cairo AzureSkiaAccelerated: 0

Important Modified Preferences

accessibility.typeaheadfind.flashBar: 0 browser.cache.disk.capacity: 358400 browser.cache.disk.filesystem_reported: 1 browser.cache.disk.smart_size.first_run: false browser.cache.disk.smart_size.use_old_max: false browser.cache.frecency_experiment: 3 browser.download.importedFromSqlite: true browser.startup.homepage_override.buildID: 20151029151421 browser.startup.homepage_override.mstone: 42.0 dom.apps.reset-permissions: true dom.disable_open_during_load: false extensions.lastAppVersion: 42.0 gfx.direct3d.last_used_feature_level_idx: 1 gfx.driver-init.appVersion: 42.0 gfx.driver-init.deviceID: 0x00ba gfx.driver-init.driverVersion: 10.0.10240.16384 gfx.driver-init.feature-d2d: false gfx.driver-init.feature-d3d11: false gfx.driver-init.status: 2 media.gmp-gmpopenh264.lastUpdate: 1448020869 media.gmp-gmpopenh264.version: 1.3 media.hardware-video-decoding.failed: true network.cookie.prefsMigrated: true network.http.atsvc.enabled: false network.http.atsvc.oe: false network.predictor.cleaned-up: true plugin.importedState: true privacy.sanitize.migrateFx3Prefs: true

Important Locked Preferences

JavaScript

Incremental GC: true

Accessibility

Activated: false Prevent Accessibility: 0

Library Versions

NSPR Expected minimum version: 4.10.10 Version in use: 4.10.10

NSS Expected minimum version: 3.19.4 Basic ECC Version in use: 3.19.4 Basic ECC

NSSSMIME Expected minimum version: 3.19.4 Basic ECC Version in use: 3.19.4 Basic ECC

NSSSSL Expected minimum version: 3.19.4 Basic ECC Version in use: 3.19.4 Basic ECC

NSSUTIL Expected minimum version: 3.19.4 Version in use: 3.19.4

Experimental Features

Download Firefox For All languages And Systems {web link} Save the file. Then;

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Mac: Open the "Applications" folder. Linux: Check your user manual.

Look for, and rename any Mozilla or Firefox folders by adding .old to them.

After rebooting the computer, run a registry scanner. Then run the installer. If all goes well, remove the OLD folders when you are done.

Can you open the about:config page?

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

Try to reset browser.uiCustomization.state via the right-click context menu to the default value.

Tried Fred's suggestion. Removed all Mozilla folders. Rebooted. Ran Ccleaner on the registry. Installed firefox from the link provided. No change.

cor-el: uiCustomization.state is set to default and has no value.

Thanks for hanging in there. This really sucks. I'm tired of IE.

Hm. That pref should have at least the default toolbar customization.

You can check for problems with preferences.

Delete possible user.js and numbered prefs-##.js files and rename (or delete) the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in current Firefox releases.

• http://kb.mozillazine.org/Preferences_not_saved
• http://kb.mozillazine.org/Resetting_preferences

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

Create a new profile as a test to check if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox