This XPath should do the trick:
//div[@class = 'y6']/span[contains(., 'subject_here')]
... , canvas_frame. . Firebug HTML, , . , Gmail , y6 .
, :
open http://gmail.com
// do the login stuff, click on login
waitForElementPresent canvas_frame
selectFrame canvas_frame
waitForElementPresent //div[@class = 'y6']/span[contains(., 'subject_here')]
clickAt //div[@class = 'y6']/span[contains(., 'subject_here')] 0,0
// do stuff you care about
: clickAt, Gmail , . "click".
, Gmail, . Selenium , Selenium .