Bug descriptions and comments use the fmt:text-to-html formatter to convert them into <p> and <div> elements, and (via id="bug-description" and class="bug-comment") special CSS to convert them to monospace.
Meanwhile merge proposal comments use <pre style="white-space: pre-wrap;">, which produces a single line of text per paragraph -- regardless of the length of the paragraph -- in browsers like Firefox 2, Internet Explorer 7 and Safari 2.0.
These should be made more consistent and cross-browser. Either:
* merge proposal comments should use fmt:text-to-html like bug descriptions and comments do, and all three should use a class= to achieve a monospace font; or
* bug descriptions, bug comments, and merge proposal comments should all use <pre>, and <pre> should be styled using {white-space: pre-wrap} as well as browser-specific properties like word-break so that it wraps in as many browsers as possible.
Tim and I had a conversation at the last Launchpad team leads sprint about getting our teams' handling of comments in sync. Some of the specifics of this bug are out of date, but the basic point of <pre> vs. class and inconsistencies between bugs and merge proposals is still relevant.