Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

In Firefox 4 and later Safe mode disables extensions and disables hardware acceleration.

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"

If disabling hardware acceleration works then check if there is an update available for your graphics display driver.

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

Thank you. I've tried all these suggestions but I still have the problem with drop down menus disappearing. I've checked that my graphics driver is up to date and tried disabling all plug ins but the problem persists. Is there anyway I can uninstall this version and go back to an earlier version which worked fine.

Corrupt localstore.rdf

• http://kb.mozillazine.org/Corrupt_localstore.rdf

Check and tell if its working.

Thank you. Have tried this but still have the same problem.

-> Create a New Profile as a test to check if your current profile is causing the problems. See:

Basic Troubleshooting: Make a New Profile

• https://support.mozilla.com/en-US/kb/Basic%20Troubleshooting#w_8-make-a-new-profile

-> If that New Profile works then you can Recover your Bookmarks and Passwords from the Old Profile. See this:

Recovering important data from an old profile

• https://support.mozilla.com/en-US/kb/Recovering%20important%20data%20from%20an%20old%20profile

Check and tell if its working.