You can check for recently installed suspicious or unknown extensions.

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window.

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

Do a malware check with several malware scanning programs on the Windows computer.
Please scan with all programs because each program detects different malware.
All these programs have free versions.

Make sure that you update each program to get the latest version of their databases before doing a scan.

• Malwarebytes' Anti-Malware:
  http://www.malwarebytes.org/mbam.php
• AdwCleaner:
  http://www.bleepingcomputer.com/download/adwcleaner/
  http://www.softpedia.com/get/Antivirus/Removal-Tools/AdwCleaner.shtml
• SuperAntispyware:
  http://www.superantispyware.com/
• Microsoft Safety Scanner:
  http://www.microsoft.com/security/scanner/en-us/default.aspx
• Windows Defender:
  http://windows.microsoft.com/en-us/windows/using-defender
• Spybot Search & Destroy:
  http://www.safer-networking.org/en/index.html
• Kasperky Free Security Scan:
  http://www.kaspersky.com/security-scan

You can also do a check for a rootkit infection with TDSSKiller.

• Anti-rootkit utility TDSSKiller:
  http://support.kaspersky.com/5350?el=88446

See also:

• "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked

DELETED

UPDATED: As of FF 29.0, a great many apparent javascript buttons on many websites are NOT working, instead the activity line at screen bottom continuously calls/displays "javascript:void" when the pointer hovers or is pressed over buttons.

This obviously means that Firefox 29.0 is NOT working right, as older FF versions of course worked properly, and MS IE 11, SlimBrowser and Chrome work properly.

There are no conflicts anywhere in the system (Win 7 64bit) nor anywhere seen via detailed inspection and troubleshooting 29.0. There are no malware, trojans, rootkits or other problems. Using or testing in FF "safe mode" is time-consuming and an exercise in the useless and ridiculous as well.

POSSIBLE VERY BAD NEWS:

This problem may be related to javascript:void and resizing snafu discussed at:

https://support.mozilla.org/en-US/questions/979358?esab=a&s=javascript%3Avoid&r=3&as=s

This may then be a built-in defect in FF 2x or FF 30, and is a major problem introduced by Mozilla, while other browsers do not have these problems.

We users need to be pointed in the proper direction to solve this situation.

JR