A previous fix for FF2 had been applied after this thread:

http://news.ycombinator.com/item?id=92629

Unfortunately, I don't think that fix ever worked in FF3 or IE7.

Also unfortunately, after some tinkering, I can't find an easy way in CSS to get the same effect in FF3 as in FF2.

The best I've achieved with a simple change is to cap the expansion with a 'max-width' on the PRE rule, like so:

  pre { max-width:60em; overflow: hidden; padding: 2px; }

(And this still is glitchy, compared to the FF2 behavior.)

I think the main difficulty is in how TABLEs expand to the size of their cells -- it's easy to fix with a DIV-based layout, in my tests. (DIV-enclosed PREs are clipped the same in FF2 and FF3; TABLE-enclosed PREs are clipped in FF2 but grow the page in FF3.)

So my long-term suggestion: drop TABLES, move to DIV-based layout. (This might be a simple change in the ARC HTML-writing code.) In the meantime, add the 'max-width' to the PRE rule to minimize the annoyance in FF3/etc.