Function keys produce unexpected results--how to reset?

[raymm]

Suddenly, my function keys (i.e., F1, F2, F3, etc.) produces results different from expected.

I.e., in Excel, F2 used to allow me to edit the cell. Now it undoes last paste.
I had set F4 in Firefox to open / close addons. Now it opens a new tab.

There are many other changes to the function key effects.

Is there some way to reset the functions keys back to default?

 

[RogerR]

1. Locate the shortcut to the program that you want to create a keyboard shortcut for.
2. Right-click the shortcut, and then click Properties.
3. In the Shortcut Properties dialog box, click the Shortcut tab.
4. Click in the Shortcut key box, press the key on your keyboard that you want to use in combination with Ctrl+Alt (keyboard shortcuts automatically start with Ctrl+Alt), and then click OK.
   
   If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
   You can now use this keyboard shortcut to open the program.

To delete a shortcut

• Right-click the shortcut that you want to delete, click Delete, and then click Yes.
  
  If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
  Note
  
  
  • When you delete a shortcut, only the shortcut is removed. The original item is not deleted.

 

[raymm]

RogerR, thanks for your reply, that is useful information, but it is not exactly what I was asking about.
My problem is not with keys for shortcuts, it is for using the Function keys inside programs. As I described above, in Excel, the function keys are not doing what I expect them to do.