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

See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

thanks for your reply, cor-el, but it did not solve my problem.... anything else i could try?

i found the solution:

   * Possible causes include using an incompatible version of JAVA or having multiple versions of Sun JREs installed. Some users have found that their problems are resolved after uninstalling all versions of Sun JRE from their computers, and then installing an earlier version.

  1. From the Start menu, select Settings, Control Panel.
  2. Double-click Add/Remove Programs.
  3. Locate all versions of Sun Java, JRE, or JVM.
  4. For each version, click Change/Remove and follow the onscreen instructions until all have been removed. 

Download Java from this link: http://java.sun.com/products/archive/j2se/6u14/index.html Click on the Download J2RE link below the second blue bar(Download JRE).To install the JRE, select the Windows platform, accept the license agreement and follow the online and onscreen instructions.

After installing the JRE, do not download updates for the JRE. To disable automatic checking for Java updates:

  1. From the Start menu, select Settings, Control Panel.
  2. Double-click Java Plug-in.
  3. Click the Update tab.
  4. Clear the checkbox next to Check for Updates Automatically.
  5. Click Apply.
  6. Click the "x" to close the Java Plug-in Control Panel window. 

· Check to be sure Adobe Reader is installed on your comptuer. If not, it is available at www.adobe.com. It is a free download, but when installing, be sure to uncheck the free toolbar that is offered. Once installed, there is a setting that needs to be "tweaked" in Adobe Reader. to do so, open Adobe Reader and click on Edit (at the top), then in the drop down menu click on Preferences, next, click on Internet (under Categories:), uncheck Display PDF in Browser, click OK and close Adobe Reader.

· Toolbars are often installed as a free add-on with software updates. Make sure you don't have toolbars attached to your web browser. If there are toolbars such as Google, Yahoo, MSN, AOL or any others, you will need to remove them through the Control Panel in Add/Remove Programs. Once you have ensured the toolbars have been removed, go to the Tools drop-down menu and click on Delete Browsing History and delete the temporary internet files and cookies. Restart Internet Explorer