This is likely a bug in Firefox, but I'm reporting it here because it affects VE, and I can't find the root cause which would be necessary for a proper upstream bug report.
When editing an article where an ordinary list (e.g. list of external links) is followed by the list of references, the reference numbers are off by the count of the list before it. E.g. https://de.wikipedia.org/wiki/Vier_Vieren?veaction=edit has 2 external links, the references start with 3. Removing that list makes the references start with 11 instead (there is another list with 10 elements in the article).
I can only reproduce with Firefox, not with other browsers.