Affected versions

• Firefox 68.8.0esr
• Firefox 76.0
• Firefox 77.0a1 (BuildId:20200430082621)

Affected platforms

• macOS 10.14

Unaffected platforms

• Windows 10 64bit
• Ubuntu 18.04 64bit

Steps to reproduce

1. Launch Firefox.
2. Bookmark a random webpage.
3. Click the “star shaped” button in order to open the “Edit This Bookmark” panel.
4. Click the “Show all the bookmarks folders” button.
5. Click the “ + New Folder” button in order to add a new folder inside the tree view (Don’t edit/save the newly created folder).
6. Click the “Hide” button.
7. Click the “Show all the bookmarks folders” button again.

Expected result

• The bookmarks folders tree view is successfully displayed.

Actual result

• The bookmarks folders tree view is displayed as broken and the only visible element is the newly created folder.
• The following error message is being outputed by the Browser Console while triggering this issue: TypeError: can't access property "title", node is undefined treeView.js:1814:9

Regression Window
This seems to be a regression.

• Pushlog: https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=0e41d07a703f19224f60b01577b2cbb5708046c9&tochange=09a4282d1172ac255038e7ccacfd772140b219e2
• I tried to track down the exact regressor and I think that "Bug 1376925 - Modernise browser_bookmarksProperties.js to use async functions and assert." has introduced this behavior.

Notes

• For further details regarding this issue please observe the attached screencast.
• It seems that only a browser restart can fix this issue (Bookmarking a new page & Removing the bookmark doesn’t seem to fix this). Also, while this issue is triggered the newly created folder can’t be created inside the tree view and the “+ New Folder” doesn’t seem to respond to click events.

Because this bug's Severity has not been changed from the default since it was filed, and it's Priority is -- (non,) indicating it has has not been previously triaged, the bug's Severity is being updated to -- (default, untriaged.)