JabRef version 5.1--2020-08-30--e023aa0
Windows 10 10.0 amd64, Java 14.0.2

• Mandatory: I have tested the latest development version from http://builds.jabref.org/master/ and the problem persists

After updating JabRef from 5.0 to the newest version downloaded from here: https://www.fosshub.com/JabRef.html ("JabRef Windows Installer"), external files linked to the bibliography entries do not open anymore. Everything worked with the same bib file in the previous JabRef version.

• "Linked files" icons are still shown near entries. However when clicking on such an icon, JabRef opens my default documents folder.
• Context menu items "Open folder" and "Open file" are dimmed.
• In the entry editor / "General" pane, when hovering over the file name element, a tooltip appears with the text "Could not find file ...".
• When adding a link to a pdf file using the entry editor (by navigating to the file), the path do the pdf file does not become relative path, as in the previous JabRef version.

The same behavior was also observed for latest development version (JabRef-5.2.msi, 2020-09-03 13:04, 178.9 MB, JabRef 5.2--2020-09-03--1283f9f).

Steps to reproduce the behavior:

1. Create any bibliography entry
2. In the entry editor / "General" pane, click "+" icon on the right of the "File" field, and select a pdf file
   The file name appears in the "File" field, the "Open file" icon appears near the entry, but the corresponding functionality does not work as described above.

Below is an example of a bibliography entry (among tens of entries in my bibliography file, all having links to pdf files, none of them work). The entry has two links to a same pdf file. The first one is relative, it was added in a previous version of JabRef, and worked as expected in the previous version. The second link is absolute, it was added in the current version of JabRef. None of the links work; the described behavior applies to both of them.

@Article{Monkk2013,
  author    = {Mikko M{\"o}nkk{\"o}nen and Artti Juutinen and Adriano Mazziotta and Kaisa Miettinen and Dmitry Podkopaev and Pasi Reunanen and Hannu Salminen and Olli-Pekka Tikkanen},
  title     = {Spatially dynamic forest management to sustain biodiversity and economic returns},
  doi       = {http://dx.doi.org/10.1016/j.jenvman.2013.12.021},
  issn      = {0301-4797},
  number    = {0},
  pages     = {80--89},
  url       = {http://www.sciencedirect.com/science/article/pii/S030147971300769X},
  volume    = {134},
  abstract  = {Removed for shortening},
  file      = {:Papers/Optimization_and_Decision_Making/Forest_Management/Spatially_dynamic_forest_management_to_sustain_biodiversity_and_economic_returns_2014.pdf:PDF;:C\:/Mytemp/dropbox/Bibliography/Papers/Optimization_and_Decision_Making/Forest_Management/Spatially_dynamic_forest_management_to_sustain_biodiversity_and_economic_returns_2014.pdf:PDF},
  journal   = {Journal of Environmental Management},
  keywords  = {Biodiversity; Cost-effectiveness; Forest management; Land use planning; Multi-objective optimization},
  timestamp = {2014.01.29},
  year      = {2014},
}