I'm not going to fault Firefox for not supporting the CSS 2.1 'word-wrap: pre-wrap', no matter how convenient it would be for me if it did. Especially since CSS 2.1 is not yet a standard, merely a late stage working draft. But I am annoyed that Firefox doesn't support the CSS2 'display: compact', since I could have used it just now.

'display: compact' is classically used (in that it is right there in the CSS2 spec as an example) to create <DL> lists where the <DT> term is on the same line as the start of the <DD> definition (or definitions, since you can have more than one). But with Firefox not supporting this, your only real option for the same visual appearance is a table.

(Please don't suggest floats.)

The Bugzilla bug is #180468, open since 2002. Mozilla not supporting <dl compact> is the impressively ancient #2055 from 1998, marked WONTFIX.

(Firefox is hardly alone in not supporting display: compact, judging from here or here; I believe that this is why the CSS 2.1 working draft quietly drops it. However, support may be on the uptick; the KHTML engine, used by Konqueror and Apple's Safari, seems to support it.)