There was a <a href="http://www.mozdev.org/" title="MozOffice">MozDev.org project</a> aiming to do this, BTW, but I don't think it's gotten too far.
And as for the features and improvements I'd like:
- <strong>A reorganized toolbar</strong>: <a href="http://bugzilla.mozilla.org/show_bug.cgi?id=148924" title="Assigned: [RFE] Reorganize Composer Primary Toolbar">Bug 148924</a>
- <strong>An expanded Insert Symbols and Characters palette</strong>: <a href="http://bugzilla.mozilla.org/show_bug.cgi?id=158965" title="Assigned: Insert | Characters and Symbols should include more code blocks">Bug 158965</a>
- <strong>Support for MathML editing</strong>: <a href="http://bugzilla.mozilla.org/show_bug.cgi?id=78128" title="New: Ability to MathML specific Stuff in Composer">Bug 78128</a><br />There's already a MathML Editor for Mozilla, but it would be nice if it were integrated into Composer. And Word already has an Equation Editor.
- <strong>Support for SVG editing</strong> (at least for SVG-enabled builds)<br />I know SVG support isn't very far along, but when it's to a decent level, I think Composer should allow you to add shapes and such, like Word allows with the Drawing toolbar.
Yeah, I know that most of these requests are a long way off, but they would be good features, IMO.