I would like to report a bug.
If there are parentheses in a URL then the link is incorrect in the preview (but not in the final page).
Example, composing an answer to a question on Stack Overflow:
Of dying programming languages [Forth] is one of the best.
The link to Forth in the preview becomes:
Platform: Firefox 3.0.6, Windows XP 64 bit, 8 GB RAM.