Steps to reproduce:

Open 100~1000 tabs.

Actual results:

Open (new) Tab1.

(WORK1) Start to write /data/data/org.mozilla.firefox/files/mozilla_components_session_storage_gecko.json.new

Open Tab2.

Still writing WORK1

Open Tab3.

Still writing WORK1

Done WORK1, but Tab2 and Tab3 are not saved.

Tap android tab list button.

(WORK2) Start to write /data/data/org.mozilla.firefox/files/mozilla_components_session_storage_gecko.json.new

Close Firefox.

Writing failed

Open Firefox.

Exist: Tab1
Doesn't Exist: Tab2, Tab3

[ Additional Issue ]
Open google.com (or wikipedia) and search anything. (URL1)

(WORK1) Start to write /data/data/org.mozilla.firefox/files/mozilla_components_session_storage_gecko.json.new

Done WORK1

Tap Google logo to main page. (URL2)

(WORK2) Start to write /data/data/org.mozilla.firefox/files/mozilla_components_session_storage_gecko.json.new

Done WORK2, but main page(URL2) is not saved.

Still (URL1) is saved.

Really?

Tap android tab list button.

(WORK2) Start to write /data/data/org.mozilla.firefox/files/mozilla_components_session_storage_gecko.json.new

Close Firefox.

WORK2 failed

Open Firefox.

Exist: google search page (URL1)
Doesn't Exist: google main page (URL2)

Expected results:

Exist: Tab1, Tab2, Tab3
Doesn't Exist: Nothing

Oh no.
How can I edit Description?

I checked files following command.

su
while do sleep 1; echo; ls -l /data/data/org.mozilla.firefox/*session*; done

I think we should use SQLite instead of JSON.

I found sources related.
https://github.com/mozilla-mobile/firefox-android/tree/main/android-components/components/browser/session-storage/src/main/java/mozilla/components/browser/session/storage

If Firefox become being able to save fast, [ Additional Issue ] can be showed being fixed.
But it is another issue.

The severity field is not set for this bug.
:007, could you have a look please?

For more information, please visit auto_nag documentation.

Hey :luckyabsoluter, thanks for reporting this.

How can I edit Description?

If you haven't figured this out since posting, there's a pencil icon at the top-right of every comment field (there's other icons there too, a tag, an arrow, and a dash which collapses the comment). You can edit the text of your comments that way.

If Firefox become being able to save fast, [ Additional Issue ] can be showed being fixed.
But it is another issue.

In your third comment and the original comment, it looks like you were meaning to link another issue but forgot to actually post it. Did you find similar ticket(s)?

Could you please post your device information?

Also, could you please reformat the original comment? I just want to make sure I fully understand what the issue is and what the steps to reproduce are.

I've also been experiencing this problem regularly, though I haven't had a chance to do much analysis as to the cause. But my changes to the set of open tabs, whether opening new ones or closing old ones, are only ever saved sporadically. Every time I open the browser, I wind up closing a dozen tabs that I closed in the last session, or (possibly worse) losing new tabs that I recently opened and am still working with.

This does seem to mostly happen in a session with a lot of tabs. But actually reducing the number of open tabs is especially problematic when they show up again the next time I launch the browser...