I asked a question on the SquirrelMail dev list about this code < http://squirrelmail.svn.sourceforge.net/viewvc/squirrelmail/trunk/squirrelma...
.
In short, there are comments in the code about Opera returning invalid values for getAttribute. Then, window.opera is used to detect Opera and make sure it doesn't get IE code.
The check for window.opera doesn't seem to be necessary for Opera to get the same code as safari and Firefox in this case and I'm not sure what getAttribute bug is being worked around. (It looks like they thought Opera had a bug because it didn't do like IE or something.)
Anyway, it was suggested that the js code might be from PHPMyAdmin (which I have absolutely no clue if it is) and that I should ask around here.
Please see < http://thread.gmane.org/gmane.mail.squirrelmail.devel/8836
and read each post.
The thread describes in more detail on what the issues are and the concerns.
If the code is really from PHPMyAdmin and the issues still exist, there may be some room for cleanup. If there really is a getAttribute bug to be worked around, the thread describes a better way than using window.opera.
If not, carry on.
Thanks.