Hi - not sure if you are still looking for help on this? Having experienced similar problems ourselves, you might benefit from the following observations:

1) The type of InfoPath template you use when creating the file from scratch determines what the form can handle once up and running. For example, you will find that a database template will not allow the form to render in browsers. Therefore you might find using a blank or standard template more flexible.

2) Depending on the method being used to launch the form, you may need to add some very basic code to the launch method. If you are launching from a SharePoint form library directly (i.e. users are clicking on the new document option at the top of the form library), this is usually safer, however if you are using a custom hyperlink on a website or SharePoint site, you need to add the following code to the very end of your hyperlink: " ' full address]'-1" to make sure the form renders in a browser. 

3) If you are using smart objects, these can sometimes upset IP forms on browser load although I find that a simple 'continue' option on the error page allows users to launch in a browser still.

4) If you are using InfoPath form functions to handle errors, you will find that the browser method does not allow these to execute in all cases. If you use basic exception handling such as managing nulls, and condition building to have one fields' contents determine other fields behaviour you will normally be ok - but anything more complicated, custom code or security matters will not function via the browser even though on the face of it the form loads error free.

Unfortunatley I have found that InfoPath 2010 was enahnced very little from 2007 and am informed this is the case for 2013 also.

I hope this helps you or anyone else watching.

Regards, Rob