I just checked the Appdata folders for more clarity.
I have 76 files in "my filters" of FF1, 796 files in "my filters" FF2 (Beta 4).
There are 717 files in "library" of FF1, 809 files in "library" of FF2 (Beta 4).
Looking at it from there and considering that I have downloaded filters in the range of 100 to FF2 it seems like all filters have been first transferred to "my filters", then doubled to other folders, after I copied the Appdata contents of FF1 to FF2 Beta 4 manually.
Would this be practicable:
1. Uninstall FF2 Beta 4, which is not functional anymore.
2. Download FF2 pro and install it.
3. Copy everything from the Appdata Folder of FF2 Beta 4 to the new Appdata Folder of FF2 pro.
4. Open FF2 pro and delete all files from "my filters".
5. Copy all files from Appdata "my filters" of FF1 to Appdata "my filters" of FF2.
Or does one of the xml-files need to be changed for step 5?
Will there be any update of FF2 release soon, so that it might make sense to step back to FF1 for the moment and wait?
Please advise.

Let the children play. :-)