Hi Wayne.
#1, Dooble just doesn't have as good auto-complete as the Mozilla apps. In Firefox etc, enter os2world and it will try os2world.com,
www.os2world.com with http and https. Not sure if a lack in Dooble or the QT5 webengine
#2, Currently the QT5 Webengine is broken when it comes to drive letters, likely needs the Windows code ported. Without a drive letter you can select a file on the drive that Dooble is installed on.
Further more, in my testing, uploading seems to be broken. Probably a QT5 Webengine problem.
#3, You have to enable search engines by going to Tools-->Search Engines... check the search engines you want to use and click the Add Checked button so they show up in the lower pane of the Dooble:Search Engines window.
Unluckily searching from the URL bar is not implemented. What you can do is highlight some text, right click, and at the bottom of the context menu, choose Search Selected Text and then your search engine.
Otherwise create a favourite with your search engine and use that.
Dooble itself is much simpler then Firefox etc, and this is a preview version and actually works amazing well with little porting. Unluckily due to war, and funding, work on fixing these issues might not happen very quick and it is unlikely to ever have the features that Firefox has.