One possibility is that a website is trying to use this method to gain additional privileges. Another possibility is that one of your add-ons is doing it.

The next time you shut down Firefox, try starting it up in Safe Mode by holding down the Shift key while double-clicking the Firefox shortcut.

A small dialog should appear. Click "Start in Safe Mode" (not Reset).

If you still get the message, it probably is generated by one of the pages you are opening. If you do NOT get the message, it probably was generated by one of your extensions.

In case your extensions might need an update to stop using old, obsolete features, you can try on the Add-ons page. Either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then, on the right side above the list, look for the "gear" button and try "Check for Updates".

Thank you for the clear instructions. I tried the solution and after the extension check for updates, the response was "no updates found". When I opened firefox in safe mode, the error message didn't appear. The error still appears when opening firefox normally.

If it works in Safe Mode and in normal mode with all extensions (Firefox/Tools > Add-ons > Extensions) disabled then try to find which extension is causing it by enabling one extension at a time until the problem reappears.

Close and restart Firefox after each change via "Firefox > Exit" (Windows: Firefox/File > Exit; Mac: Firefox > Quit Firefox; Linux: Firefox/File > Quit)

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

I followed your excellent instructions. I disabled all the add ons and then went through each add on enabling, exiting foxfire, starting foxfire without a problem and then doing the next. Once I was done, without any other fixes, when I start foxfire the error msg box no longer appears.

Thanks for your help.