The earlier fix (ef7896ab5f) migrated 9.0.x's "<id>-default" prefs
forward to the refactor's new "<id>" key, but that left 9.0.x and 10
beta keying differently in treePrefs.json, so switching between versions
always reset 9.0.x to defaults.
Put the `-default` suffix back so Z9 and Z10 read and write the same
key, and migrate any unsuffixed `<id>` data written by an earlier beta
back to `<id>-default` on first load. The migration runs once per
process and can be removed in a future release once beta users have all
updated.
https://forums.zotero.org/discussion/131653/zotero-10-beta-5-reinitializes-the-columns-in-main-pane