The problem is that the browserName is coming from your secondary data source and Tableau won't pass that through to the URL filter. So even though Tableau will let you filter on browserName as a dimension (which is new in v8), the browserName is not truly in the level of detail of the view and isn't available to be passed through as a URL action.
Looking at your data it doesn't seem like you can bring browserName in to the primary and retain the level of detail (it would come across as an * because there are multiple browserName's for each date & counry, so one option might be to swap the primary and secondary for the Counter view and adjust the calculations appropriately. If that doesn't work, another option would be to build a scaffold source that has enough detail that you can have the level of detail necessary to use in the URL action.
Jonathan, thanks for the advices. Swap the primary and secondary does not work for me but I'll look for alternatives for my use case.