Are you talking about the Bookmark and history drop-down in the Menu bar?

• Create a screenshot of the problem

The image shows the toolbar while in Customize mode. As you can see the Bookmarks icon is 6th from left and History icon is to the right of that. When I exit Customize only the History icon appears. If I return to Customize they both appear. This was happening all morning. I tried safe mode, etc. but did NOT do a Reset since that would undo all my extensive customizations. However, after closing and opening the browser a few more times all of a sudden it's back to normal and both icons are available! So while the problem now is gone it's a mystery as to what was going on.

Try drag and drop the history icon in another place of your toolbar, only for test.

Maybe the problem can be the localstore.rdf, it can be corrupted, first uhide the hidden files and folder:

• http://kb.mozillazine.org/Show_hidden_files_and_folders

Then go to your profile folder, close Firefox, delete the localstore.rdf file:

• Profiles

Also:

• Preferences won’t save
• http://kb.mozillazine.org/Preferences_not_saved

I would have tried it if it hadn't suddenly resolved itself, so I can no longer test if that would work. But I'll keep your response re. localstore.rdf for future reference. Thanks for your help!