- In a new (or refreshed) Firefox profile, have just one window and load this page
- https://addons.mozilla.org/addon/refined-github-/ add the extension
- https://addons.mozilla.org/en-US/firefox/addon/duplicate-tabs-closer/ add the extension
- https://addons.mozilla.org/addon/simple-tab-groups/ add the extension
- about:preferences
- ☑ Restore previous session
- about:addons
- Extensions
- disable Refined GitHub
- preferences for Duplicate Tabs Closer
- scope: all windows
- in the toolbar, click the Simple Tab Groups button to reveal its menu
- manage groups
- create two groups, A and B
- close all tabs except the tab for this page
- open https://bokut.in/freebsd-patch-level-table/#stable/12 in a new tab, then view the tab
- open seven of the linked pages into new tabs
- move tabs 6–9 into group B (click tab 9, Control-click tab 5 to select all four, then use the context menu)
- similarly, select tabs 2―5 (beginning with tab 5), move all four at once into group A – leaving this GitHub Gist page alone visible (the other eight tabs hidden) in an isolated, non-grouped tab
- open a new window (window 2)
- load group A
- open a new window (window 3)
- load group B
- close windows 2 and 3
- enable Refined GitHub
- open a new window (window 2)
- load group A
- observe the red alert from Duplicate Tabs Closer, but make no attempt to de-duplicate
- observe, but do not click on, the titles of all four tabs
- close window 2
- load group A
- observe the losses from group A – where previously all tabs were apparently titled, now some are New Tab with no content
- about:addons
- disable Refined GitHub
- open a new window (window 2)
- load group B
- close window 2
- load group B
- free from loss – each of the four tabs is titled and its content can be loaded.
The bug begins to bite in window 2 at step 27, however an end user is unlikely to realise the problem because all tabs appear to be titled.
After closing a bugged window, non-loaded tabs that were previously titled are lost – each New Tab has no content.
With any two or more conflicting extensions enabled: it's possible to avoid loss by reloading all visible tabs within the bugged window – before the bugged window is closed.