How do I open a generated html file in Vaadin OSGi, deployed on Felix

I have a Vaadin OSGi demo coming up and cannot find how to use a dynamically created html file.
I’m using Felix as the OSGi framework.
The UI consists of a tabsheet with for each installed bundle a tab.
The code in one of the tabs generates an html file, that need to be opened in a separate pop-up window.

When I run that bundle as a non-OSGi Vaadin app this works fine. I’m using
VaadinService.getCurrent().getBaseDirectory().getAbsolutePath()
to get the physical path and file
rsgsession.html
is then written into the resource subfolder. The html file can then be opened with this url:
http://localhost:8880/coreserver/VAADIN/themes/coreserver/rsgsession.html

How can I do this similar in OSGi? I cannot find a physical directory where the html file can be written into.
The main app is opened with
http://localhost:8888/uiconsole

I like to be able to open my html file using e.g
http://localhost:8888/uiconsole/rsgsession.html

Any help would greatly be appreciated!