Where do these errors appear: do you get popup/alert dialogs, or do they display within the web pages?

In case one of your extensions is involved, could you test in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Diagnose Firefox issues using Troubleshoot Mode.

If Firefox is not running: Hold down the Shift key when starting Firefox. A small dialog should appear. Click "Start in Safe Mode" (not Reset).

If Firefox is already running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

Not all add-ons are disabled: Flash and other plugins still run

After Firefox shuts down, a small dialog should appear. Click "Start in Safe Mode" (not Reset).

Any difference?

3-bar help menu -> add ons -> extensions all the extensions i had were junk anyway. i just removed them all & now Mozilla seems to work fine. thanks for your help.