Hello,

Try disabling graphics hardware acceleration while you are in safe mode, and then restart normally.

1. Click the menu button and select Options
2. In the Firefox Options (or Preferences) window, click the Advanced tab, then select General.
3. In the settings list, you should find the Use hardware acceleration when available checkbox. Uncheck this checkbox.
4. Now, restart Firefox normally and see if the problems persist.

Additionally, please check for updates for your graphics driver by following the steps mentioned in the following Knowledge base articles:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems
• Upgrade your graphics drivers to use hardware acceleration and WebGL

Did this fix your problems? Please report back to us!

In the Advanced Tab, neither General nor the other tabs have a Use hardware acceleration when available checkbox on the version I'm using -- the latest update of T-bird and Yosemite.

Hi rbfreemontana, this thread refers to Firefox on Windows. Since you are posting about Thunderbird on Mac, it would be less confusing to continue with your recently posted question here: https://support.mozilla.org/questions/1038041

Thanks Jscher! Sorry for my confusion.