Wrong Favicons in Firefox

Solution 1:

Close firefox, delete %AppData%\Mozilla\Firefox\Profiles\<your profile>\favicons.sqlite

This is easier to do than peqhusus's solution, but it does mean you'll lose all cached favicons and have to reload your bookmarks to get the icons again.

Solution 2:

This may not be the best solution if you are only slightly annoyed...

What I usually do when this happens is go to

Bookmarks --> Show All Bookmarks --> Import and Backup --> Export Bookmarks to HTML file

Then open the bookmarks file, find the corresponding bookmark entry, then change ICON_URI="{URL}" ICON="data:image/png;base64,{data}

to the URL of the icon and the base 64 encoded icon in png format

Then import the modified bookmarks file back into Firefox