Add-ons that don’t have BrowserActions are behaving normally.
Add-ons that have BrowserActions that don’t have Panels are behaving normally.
Non-panel-based features of add-ons whose BrowserActions open Panels work.
Clicking those BrowserActions that are supposed to display panels has the effect of (visually) toggling (what is apparently) active/inactive state of the button, but no panel appears.
All add-ons that have BrowserActions with panels are affected by this. These include facebook.tracking.exposed, Persistent Highlighter, Archive URL, NoScript, PageSaver WE, Search All Tabs.