I just found that Opera 10 can also use Greasemonkey script, but it is actually User JavaScript. Therefore, I tried to use GMail HTML Basic Enhancement. But failed. This is because one needs to enable User JavaScript on HTTPS protocol first.

To use the User JavaScript, first set the folder based on this article, and remember to restart.

Then, at the address bar enter “opera:config”, search for “User JavaScript on HTTPS”, enable it. Yeah!