Try to reset the Windows icon cache.

1. Open the Task Manager (Shift+Ctrl+ESC)
2. In the Process tab, right-click on the Explorer.exe process and select End Process.
3. Open the file picker via "File > New Task (Run)" and click the Browse button.
4. Type or Paste %USERPROFILE%\AppData\Local in the File name field (AppData is a hidden folder).
5. Select the file IconCache.db and use Delete in the right-click context menu to delete the file.
6. After the IconCache.db has been deleted, start a new explorer.exe process via "File > New Task" to get the desktop and Taskbar back.

• It is possible that the file IconCache.db is a hidden file and in that case you need to enable viewing hidden files. You can verify that you can see the file before doing the above mentioned steps.

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

I, too, had the same problem. I discovered by accident that changing the display size to medium (Control Panel -> Appearance and Personalization -> Display) makes the icon normal.

The easiest solution is to follow eleroy44's solution to change the display size to medium. If you find that everything is too big, as I did, then when you change back to the smaller size the firefox icon will still be ok. I guess doing this clears the icon cache as part of the process.

When I initially tried to follow cor-el's solution I was unable to find the IconCache.db file. I tried viewing hidden and also system files, no sign of it.

Firefox is still my default browser. I have done all steps as per your instructions given in firefox. But it makes effect for some time. I mean I am deleting IconCache.db file & it changes the html file icon for few minutes but than again it shows white paper icon. It is my request is their another permanent solution? Why this problem is occurring? Is their any virus on my laptop? Please help me to sort this problem?

Please explain in detail steps how to do it. Will Firefox icon come back & not change after some time on .html file.