If you just change the <title> tag it should change the page title (firefox), and nothing "inside the forum". So it's hard to tell what actually went wrong from your description... can you elaborate?
i did what u said , but it changed the topic title inside the forum
like : MyBB 1.4 General Support / Forum Title on every topic ? - FuzzyShare
i will add a screen shot
just a sec
You edited the wrong template in a wrong way then...
The region you marked is in the <body> of the page, when you were supposed to change the <title> which is in the <head> of the page...