By default show only topics field in search
Remove "Jump to issue N." which is useless (it's enough to open .../issueNN)
Enable "collapse" plugin.
Do not show 'Attachments' after a message if the message contains a file that has been removed from the issue
Remove 'Submit changes' button.
Make the 'Extra information' section (<fieldset>) hidden by default, make the label a button to show the extra informations by clicking on it.