Start Firefox in Safe Mode {web Link} by holding down the <Shift>

(Mac=Options)   key, and then starting Firefox. Is the problem still there?

Starting in safe mode appears to have fixed that issue. Does that mean that I would have to run FF in SM all the time?

No, Not required all the time. Or you can do restore your broswer. So automatically this issue will be fixed. Due to some cache and cookies issue. For few websites, this type of problem arises.

What are the steps to restore the browser?

The Refresh feature (called "Reset" in older Firefox versions) can fix many issues by restoring Firefox to its factory default state while saving your bookmarks, history, passwords, cookies, and other essential information.

Note: When you use this feature, you will lose any extensions, toolbar customizations, and some preferences. See the Refresh Firefox - reset add-ons and settings article for more information.

To Refresh Firefox:

   Open the Troubleshooting Information page using one of these methods:
       Click the menu button New Fx Menu , click help Help-29 and select Troubleshooting Information. A new tab containing your troubleshooting information should open.
       If you're unable to access the Help menu, type about:support in your address bar to bring up the Troubleshooting Information page. 
   At the top right corner of the page, you should see a button that says "Refresh Firefox" ("Reset Firefox" in older Firefox versions). Click on it.
   Firefox will close. After the refresh process is completed, Firefox will show a window with the information that is imported.
   Click Finish and Firefox will reopen. 

Did this fix the problem? Please report back to us!

Thank you.

I think I misspoke. My issue is not fixed. The calendar doesn't change with a hovered mouse it changes when the mouse is moved side to side

Hi, please try making a New Profile : Make a new one and test ...:

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles

If is your Profile :

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

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