Comment 24 for bug 608631

You're wrong, a "monospace" font style will only apply to characters for which it is relevant:

It DOES NOT force any character to be monospaced, notably not those for which this is opposed to their semantics.

So Chromium or Chrome are PERFECTLY RIGHT (they absolutely don't have any bug here !) when it displays the NNSP has a narrow character, escaping the default rules applicable to other characters that don't have any explicit differences of semantics between the case where they are styled in a variable-width or monospaced font.

The "monospaced" font style in CSS is a hint that is meant only to select appropriate fonts, where it is relevant and multiple fonts are candidates. Some scripts (Arabic for example in some of its ligatures, or Japanese kanas which normally used half-width characters instead of square characters used in kanjis) will be definitely incorrectly represented, if they are rendered with monospaced glyphs only (and that's why East-Asians have their own set of fullwidth punctuations, separated from the standard ponctuations like dot and comma).

Characters have semantics, and if this semantic includes width restrictions, they should be preserved as much as possible. If this is not possible, then use a reasonnable "compatibility" fallback for the rendering, but DO NOT change the encoded abstract characters.