If you give TDs a CSS width and then use colspan, Explorer Windows still uses the declared CSS width for the content of the colspanned TD.

Test page. Workaround is not included.
Reported by ppk.

Giving a <button> element a margin-bottom makes the text drop down.

Test page. Workaround is not included.
Reported by ppk.

For nested boxes IE doesn't add the outer box padding and the inner box margin, as all other browsers do.

Test page Workaround is not included
Reported by: Daniel Bleisch.

The CSS 'bottom' property can be used to place an absolutely positioned element relative to the bottom of the containing block. When 'top' is also specified, the element should stretch from 'top' to 'bottom'. However, when both are specified, IE ignores 'bottom' and instead bases the height of the element on its contents (shrink-to-fit).

IE similarly ignores the CSS 'right' property when 'left' is specified.

Only IE 6.0 and Firefox 1.0 tested. No pure CSS (non-javascript) workaround found yet.

Test page Workaround is not included
Reported by: Justin Schiller.

In Explorer Windows an element both floated and cleared is ignored by a subsequent float: the latter is positioned higher than the former, and overlaps it.

Explorer Mac and Opera don't get it quite right, either, but they're not as bad as Explorer Windows.

Test page Workaround is not included
Reported by: Bruno Fassino.

When the font of a page in an iframe is resized, Explorer Windows seems to retain the line-height of the previous font size.

Test page. Workaround is not included.
Reported by ppk.

IE/Win does not respect a set line-height in presence of an inline image shorter than the line-height.

Test page Workaround is not included
Reported by: Bruno Fassino.

When navigating between named anchors in IE, the window.location object changes to reflect the change in the URL. This is correct. However, the window.location object should also change when you use the back or forward buttons, or the history.back() and history.forward() methods, to move between these anchors, and in IE 6.0 and IE 6.1, it does not.

Opera has exactly the opposite bug: it never shows the hash.

Test page Workaround is not included
Reported by: Isaac Z. Schlueter.

Internet Explorer on Windows completely ignores closing LI tags.

This means that if the list item contains a block level link, the blank space after the LI will be rendered as a blank line.

It also means that if elements are nested within the list, but not within a LI (this is invalid HTML, but people still do it), IE will treat them as if they are in the preceding LI. This modifies both the DOM and the response to CSS.

Test page Workaround is included
Reported by: TarquinWJ.

The box model of a td turns out to be unchangeable in Explorer (Win and Mac), Mozilla and Opera. Explorer Mac forces it into the traditional model, while the other browsers force it into the W3C box model.

Therefore you can't switch the box model of a td, something that is possible for any other element.

Explorer Windows, though, switches the TDs to the correct box model when you use table-layout: fixed. Unfortunately this does not work in the other browsers.

Test page. Workaround is included only for Explorer Windows.
Reported by ppk.

When clipping an element in Opera any underlaying content becomes visible, but does not allow user interaction. The clipped region is somehow still obstructing the content.

Bug is at least present in version 7.5x and the latest version 8 previews.

On a side note: the testpage also reveils a nice IE-thingy: the clipping is not applied through CSS which might make you believe that IE is not capable of clipping through CSS. However, when the same style is applied using javascript it works!

Test page Workaround is not included
Reported by: Tino Zijdel.

If you use appendChild to move a table row to the end of its table (tbody), Explorer 5 Mac will hang up.

Test page Workaround is included
Reported by: TarquinWJ.

When an element has a CSS rule applied using 2 ID-selectors, eg.
#element1 #element2 { background-color: red; }
it is impossible to dynamically change those style-properties through javascript.

Applies at least to Opera 7.5x and latest 7.6 previews.

Test page Workaround is not included
Reported by: Tino Zijdel.

Using the :first-letter selector (such as to do drop-caps) crashes IE 5.5 and 6.0 WinXP when that first letter is part of an underlined link which is visible on-screen.

Reported to MS in February 2004 - may be fixed in SP2, but I haven't been able to verify it.
:first-letter doesn't work in IE 5.0 Windows, so that browser doesn't crash.

Rare in that this crashes the browser, rather than just displaying in a funny manner.

Test page Workaround is not included
Reported by: Dave Polaschek.

In a frameset a body {overflow: hidden} declaration is carried on to the next page.

Test page. Workaround is included.
Reported by ppk.

The getAttribute() method allows you to read out any attribute from any tag. Except in Opera 7.54 and lower, which refuses existing attributes on the wrong tag.

Test page. Workaround is not included.
Reported by ppk.

Explorer 5.5 Windows and below see an imported print style sheet as a normal screen style sheet.

Test page. Workaround is not included.
Reported by ppk.

When using overflow: auto for an element inside a page, the page nonetheless may become long enough to contain the entire content of the element, even though part of it is hidden. This creates unwanted scrollbars.

Test page. Workaround is not included.
Reported by ppk.

When placing an absolutely positioned element in a relatively positioned one, Explorer 5.0 Windows may calculate the left relative to the browser window instead of to the relatively positioned element.

Test page. Workaround is included.
Reported by ppk.