I have an .aspx page and I'm trying to locate a textbox via the selenium UI. The id is: `p_lt_ctl01_pageplaceholder_p_lt_ctl00_SignUpFree_txtFirstName`

I've tried: `id=*._txtFirstName`
and: `id=glob:*_txtFirstName`

Is there a better way other than CSS to locate a textbox whose id may change each time it's compiled?