Problems with Copy/Paste?

Fix Firefox...

Tools menu
Options
Content tab
Enable Javascript (presumed checked)
Advanced button on same line
Uncheck "Disable or replace context menus"

or...
Enter some text in the comment box, choose Google as my profile, click Preview, and then click Edit. After that I am able to cut, copy and paste as usual, and my profile name shows up in the "Comment as" box (i.e. no need to log in; it recognizes that I'm already logged in).