2052960 - "Restore previous session" appends to the Smart Window new tab instead of overwriting it

Status: VERIFIED FIXED

(Core :: Machine Learning: Frontend, enhancement)

Description

[Giulia Cardieri (:giulia)]

When Smart Window is the user's default and you restore the previous session manually (History -> Restore Previous Session), the restored tabs open alongside the empty Smart Window new tab instead of replacing it. In a Classic window the restore correctly overwrites the initial new tab.

Steps to reproduce:

1. Enable Smart Window and set it as the default (browser.smartwindow.enabled + browser.smartwindow.isDefaultWindow), signed in, with browser.startup.page = 1.
2. Open a few tabs and quit.
3. Start Firefox — it opens a Smart Window showing the new tab.
4. History menu → "Restore previous session".

Expected: the restored session replaces the new tab (same as a Classic window).
Actual: the new tab is kept and the restored tabs open separately.

Root cause:
SessionStoreInternal._prepWindowToRestoreInto decides whether restore can overwrite the current tabs by checking each tab's URL against a list of "home pages" (about:blank + HomePage.get()):
https://searchfox.org/firefox-main/source/browser/components/sessionstore/SessionStore.sys.mjs (see _prepWindowToRestoreInto, the homePages / removableTabs logic)

A Smart Window's new tab is chrome://browser/content/aiwindow/aiWindow.html, which isn't in that list, so it's not treated as removable. As a result canOverwriteTabs stays false and the restore appends the previous session's tabs instead of overwriting the new tab. A Classic window's initial tab (about:home) is in the list, so it gets overwritten.

Comment 1

[Giulia Cardieri (:giulia)]

Attachment: Bug 2052960: Add Smart window new tab as an overwrittable page on restore previous session

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/1189cacea8d4
https://hg.mozilla.org/integration/autoland/rev/e48087da534d
Add Smart window new tab as an overwrittable page on restore previous session r=sthompson

Comment 3

[amarc]

https://hg.mozilla.org/mozilla-central/rev/e48087da534d

Comment 5

[Rares Doghi, Desktop QA]

Verified as fixed in our latest Nightly 155.0a1 (2026-08-10)

Comment 6

[Rares Doghi, Desktop QA]

Updating the main status flag.