Hello H W,
We are not aware of such problem except for when thisis done on purpose e.g if you have a button and you return false in its client handler, differences might occur under IE and FF and this also might happen when using the UseSubmitBehavior
If you need further assistance, please start stripping down code until you isolate the problem. Once you do this, just share some reproduction code here and I will built up a test demo on my side and do my best to help.
All the best,
the Telerik team