It stores the presence or absence of a favicon in History. If you want to reset it, clear your History. Here is a comprehensive FAQ.
why doesn't the favicon for my site
appear in IE7?
This is a re-posting of
a post originally published on
2007-03-01. The original can be found
here. This version has been updated to
match what is currently reality.
When I was at Microsoft, I was the
developer tasked with fixing the
Favicon story for IE7. The original
IE6 behavior was to download the
favicon once--when a user made a site
a Favorite. I do not want to go too
deep into the details of how this
craziness works, but the key piece of
information to understanding why it
seemed so broken is this: a mapping
between the url of the site the url
for the site's Favicon would be stored
in IE's History database and the
actually bits of the icon would be
stored in the temporary Internet files
folder. Thus, if you cleared your
history or your cache, or the item
expired out of either one, the icon
would be gone forever.
Fast-forward to IE7. It has been over
two (three?) years since IE6 shipped.
We want to implement tabbed browsing,
and we want the tabs to display the
correct Favicons. So I updated the
Favicon code to always download the
icon on a first visit. The code also
remembers if there is no Favicon (404)
or it was invalid in some way
(ExtractIcon() failed).
Here is a Mini-Faq (with one bonus
question at the end) that I wrote
while I was at Microsoft:
Q: How do I make a favicon appear for
my site in IE7?
A: There are two ways.
The first is to put a file in the root
of your domain called favicon.ico. The
second is to use a <link> tag with the
rel="shortcut icon" value and the href
value set to the URL for the Icon you
wish to display.
Q: How often does IE download the
favicon?
A: IE will download the icon
when a user first visits the site. The
icon is stored in the Temporary
Internet Files folder on the client
machine. Additional metadata about the
favicon is stored in the user's Url
History database. If either store is
cleared, or items relating to the
favicon have naturally expired, then
the icon will be downloaded again on
the next visit. If more than one page
(or site) shares the same favicon, it
is only downloaded once. IE takes
great pains to download the icon as
few times as possible to reduce load
on the server.
Q: I see the wrong favicon for some
sites I visit. How do I fix this?
A: If the history database has become
corrupted in some way, this can
happen. The simplest solution is just
to use Delete Browsing History (on the
Tools menu) to clear the cache and the
history store.
Q: I put a favicon.ico on my site as
you described, but it still doesn't
appear.
A: It must actually be a .ico
(an Icon) file. Bitmaps, pngs, gifs,
etc, will not work. IE7 will download
your favicon to the Temporary Internet
Files folder and call ExtractIcon() on
the file. If this fails, we will show
the default icon instead of your
favicon.
Q: I verified that my favicon really
is an icon, but it still doesn't
appear.
A: Since IE loads your icon
out of the Temporary Internet Files
folder, it must be able to actually
store it there. If you are setting the
no-cache directive for the icon file,
then IE will not be able to display
your icon and will display the default
icon instead. You can use Fiddler to
verify.
Q: How do I create a different favicon
for every page on my site?
A: Put a
different tag on each page, pointing
to a different icon.
Q: I changed my site's favicon to a
different icon, but the old one still
shows in IE. How do I force IE to
update?
A: If you just put the
favicon.ico file in the root of your
domain, IE doesn't have any way of
knowing if it changed. To force an
update, you need to use a tag and
point to a different filename than you
previously used. The current filename
is compared against the known filename
stored in the Url History database.
When IE sees the filename has changed,
it will download your new icon.
Alternatively, you can ask your users
to clear their history and cache
(Tools->Internet Options->Delete
Browsing History), which will also
force IE to download the new file.
Q: What is still broken?
A: Two
things:
- If you specify an
alternate location via tag, the
href member must be fully-qualified
and does not respect the tag.
- The tag must have "shortcut
icon" as the rel value, but this is in
violation of the W3C spec that says
whitespace in the rel tag denotes a
list of values. IE treats "shortcut
icon" as a single value. Luckily this
still works for other browsers who see
"shortcut" and ignore it and only pay
attention to the "icon" string.
That should cover most of the
questions I've received about favicons
in IE7. If you have more questions,
feel free to ask.
