Uninstalling breaks file type associations or icons
From MozillaZine Knowledge Base
Uninstalling Firefox can break file associations or icons in some cases. This article describes how to get file type associations and icons back to another browser on Windows, if you have uninstalled Firefox while it was set as the default browser .
Before trying these steps you should first make sure you have another browser set as the system default. You can usually open whichever browser you want to be default and look through its options for the button that sets it to default. The default browser article describes other methods.
If setting another browser as the default doesn't completely restore things, you can set file associations individually.
Windows XP and earlier:
Important: If Firefox is currently installed and set as your default browser, do not use these instructions to choose another icon for filetypes associated with Firefox. Step 4 can cause a problem if you choose the "wrong" icon, and if you have Firefox set to check whether it is the default browser. If you do not choose the second icon embedded in Firefox to represent .html files, Firefox will complain that it is not the default .