QTP problem: properties are not recognized for test runnig on Firefox

Condition: Quick Test Pro v.10; Mozilla Firefox v.3.0.5
There is the next fragment in VB-script test
...
1.  SystemUtil.Run browserPath, urlMainPage, "", "open"
2.  Browser("Index:=0").Page("title:=WWW-Код").Sync
3.  Set obj = Browser("Index:=0").Page("title:=WWW-Код").Object
...
This test is well run with IExplorer,
but I have got problem with Firefox in third script line (see qtp-debugger error message):
'Cannot identify the object [Page] (of class Page). Verify that this objects properties match an object...'

Why does not recognize the Object property of Page for Firefox?