The upgrade to Zotero 5 didn't migrate my passwords for neither zotero.org nor for my webdav storage, and when I tried to enter them again in the preferences dialog I found that the dialog is cut off, and even enlarging the window doesn't show the rest of the dialog. Hence I couldn't access the field to enter the webdav password. Here's a screenshot (don't know how to attach pictures here):

https://imgur.com/a/eHJpU

This is zotero 5.0.28 on Linux with XFCE desktop. As a workaround I tried all the possible GTK themes and found one which is a bit more compact so that the password field was in view. Another workaround is to reset my display DPI from 157 (which is correct for my laptop screen) to "default" (which makes everything too small) and then the whole dialog shows up (but is hardly readable).