Does this happen in the same window, or is the toolbar missing in new windows, or both?

You mention that it may only happen every couple of weeks, suggesting this pre-dates Firefox 36. How long would you say it has been happening?

Do you have any add-ons or custom style rules that affect the layout of the toolbar area? Examples would include Classic Theme Restorer, full themes, or a userChrome.css file.

This might help if you do a clean installation to FireFox :) Let me know if it works, or if you don't know how to here; Hello,

Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove Firefox program files and then reinstall Firefox. Please follow these steps:

Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from mozilla.org (or choose the download for your operating system and language from this page) and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (or open the Firefox menu and click the close button ).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
   • Mac: Delete Firefox from the Applications folder.
   • Linux: If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder firefox in your home directory.
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

WARNING: Do not use a third party uninstaller as part of this process. Doing so could permanently delete your Firefox profile data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. These cannot be easily recovered unless they have been backed up to an external device! See Back up and restore information in Firefox profiles.

Please report back to say if this helped you!

Thank you.

Has been doing this for about a year. PC is a little over a year old, preloaded with Win8. Only happens when opening Firefox. I seldom turn PC off, have game running almost 24/7 when I'm not on PC. Have NO stupid add ons like Ask or Yahoo toolbars. I will not uninstall reinstall. Should be fixed by programmers. Had same problem on older Win XP machine.

Bugs do get fixed once the cause of the behavior is identified. However, it is difficult to track down the culprit when the behavior is so random. If you can spot more of a pattern, that would be really helpful.

Only happens when opening Firefox. Sometimes more than once a day.

Do you have extensions that might be causing this or possibly updating extensions or updating of Firefox?

You can try to rename (or delete) the xulstore.json file in the Firefox profile folder.

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox

There are other things that need your attention.

Your System Details List shows multiple Flash plugins.

• Shockwave Flash 17.0 r0
• Shockwave Flash 16.0 r0

You can find the installation path of all plugins on the about:plugins page.

• http://kb.mozillazine.org/Issues_related_to_plugins#Identifying_installed_plugins

You can check the Flash player installation folder for multiple Flash player plugins and remove older version(s) of the plugin (NPSWF32) and possibly (re)install the latest Flash player.

• (32 bit Windows) C:\Windows\System32\Macromed\Flash\
• (64 bit Windows) C:\Windows\SysWOW64\Macromed\Flash\