GWT project debug crash

Question

I build my GWT project successfully. After dubug when tried to run the generated URL in browser the following error comes.

[ERROR] The value gecko was not previously defined. 
[ERROR] Line 35: Unexpected exception while processing element 'set-property'

the set property is defined as :

<set-property name="user.agent" value="ie6,ie8,safari,opera" />

Must be some silly mistake please point out.

other error reported in console are:

[ERROR] Failure while parsing XML
[ERROR] Unexpected error while processing XML

Unexpected exception while processing element 'inherits'

Answer 1

Add gecko1_8 for Firefox support.

<set-property name="user.agent" value="gecko1_8" />