Affected versions
*68.0, 69.0b5, 70.0a1 (2019-07-16)

Affected platforms

• Windows 10, macOS 10.13, Ubuntu16.04;

Steps to reproduce

1. Launch Firefox access any random page;
2. Click on the Star button to bookmark it;
3. Open the Dropdown for the Folder section;
4. Click on the Choose option;
5. Click on the New Folder button multiple times.

Expected result

• No glitches occur;

Actual result

• while the new item is in view the name_frame overlaps the scrollbar;
• after the new item is no longer in view it jumps out of the section's bounds.

Regression range

• reproducible with 25.0a1

Additional notes

• attached screenshot with the issue;
• probably a dupe, but was unable to find any logged issue;

This may actually be a dupe indeed...

In general users don't have many bookmarks, and at most a couple levels deep.
Surely there may be cases like this, but not worth prioritizing.