A student that I was helping deal with his large Zotero library (see https://forums.zotero.org/discussion/64912/large-zotero-library-runs-really-slow) has another problem. In trying to deal with the library running so slowly, he uninstalled and reinstalled Zotero and FF and eventually ended up with two separate Zotero databases under old and new FF profiles. There are a lot of similarities between the databases, but there are significant differences, and he has somehow managed to make changes to both of them.

Is there a good way to go about merging these two databases? I have copies of the two data folders to experiment with.

I did read the discussion at https://forums.zotero.org/discussion/comment/266924, but I think that this is a separate issue.