1979526 - Since this week's Firefox Dev. update when FF is closed tabs will - or won't load randomly when the browser is started up.

Status: NEW

(Firefox :: Session Restore, defect)

Description

[Chris Moland]

Attachment: ChrisMoland_FirefoxDevBrowserNotLoading_July26_2025_1106h.txt

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:142.0) Gecko/20100101 Firefox/142.0

Steps to reproduce:

This is happening in FF Dev (since 142.0b2) and FF regular (141) and across multiple physical (and a virtual) machine.

FF Dev is now 142.0b3 and the issue is persistent.

Long story short, this time loading either FF version my tabs will load, the next time they won't. But not A/B. It may not load five times in a row, then load. Or... load 3 (pick your number) times in a row and then stop working again. It is intensely disruptive to my workflow.

Hardware acceleration is disabled. Theme is Default.

I will put the link here to the "Ask a question" submission I made on Mozilla Support to save time as many details are there as well.

support.mozilla.org/en-US/questions/1524978#answer-1751914

I thought, at first, this was exclusively an issue with an extension, but even then the results I keep getting back are completely random.

To repeat this behaviour only started with 142.0b2 (Developer edition) this last week, and later in the week I discovered that it was also happening in regular FF (141) as well.

I have totally run out of ideas on how to fix it.

The extensions I have loaded and active now are - generally speaking - working fairly consistently, but I still have it having tabs not load multiple times here and there.

I pulled the Troubleshooting Information from July 24th, before I started working on the issue in earnest and am attaching it here, along with the troubleshooting information from right now (July 26th @11 AM MDT) in case that helps you to compare them.

Actual results:

I thought, at first, this was exclusively an issue with an extension, but even when I disable all of them and add them back the results I keep getting back are completely random on which.

Expected results:

Tabs from previous sessions, and pinned tabs, should load consistently.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Firefox::Tabbed Browser' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Comment 2

[James Deeman]

Same issue. Thought it was isolated to my work machine. I have now experienced it on my home machine too. Tabs are all there, but won't present the page nor appear to query the server.

One thing I have noticed is that when I close a singular FF window, trying to run it again states that Firefox is already running. Like a process has stalled. I am on 141.0.

I have tried disabling extensions as well as turning off hardware acceleration.

Comment 3

[Chris Moland]

Confirming that I have the same behaviour @James Deeman reports about getting a "Firefox is already running" message some times when closing browser windows.

Comment 4

[Dão Gottwald [:dao]]

(In reply to Chris Moland from comment #0)

Expected results:

Tabs from previous sessions, and pinned tabs, should load consistently.

Moving this to session restore.

Comment 5

[BugBot [:suhaib / :marco/ :calixte]]

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

For more information, please visit BugBot documentation.

Comment 6

[Ina Popescu, Desktop QA]

Attachment: log.txt-main.4172.moz_log

While using Firefox Dev 142.0b9 on Windows 10 with “Open previous windows and tabs” enabled, I encountered the error “Firefox is already running, but is not responding” on startup.

Steps to reproduce:

• Open multiple tabs
• Reload some tabs
• Close Firefox with the X button
• Reopen Firefox
• Repeat several times

After a few restarts (number varies), the error appeared.

I’m not sure if this is the same issue reported here or caused by something else ( network issues or a slow PC), because I’ve seen the same error while testing 140.0b9. I’ve attached logs recorded with about:logging for reference. Therefore I'm not changing the status for now.

Comment 7

[Sarah Clements [:sclements] | PTO until Jan 5th]

Hi Ina, since you're able to reproduce this are you able to get a regression window going further back than 140.0b9?

Comment 8

[Ina Popescu, Desktop QA]

(In reply to Sarah Clements [:sclements] from comment #7)

Hi Ina, since you're able to reproduce this are you able to get a regression window going further back than 140.0b9?

I looked manually for the regression range and narrowed it down to this pushlog: https://hg.mozilla.org/releases/mozilla-beta/pushloghtml?fromchange=312594901b5e9c1f83375e5c682e3fae6a63ff77&tochange=d64304506c8d97f6ea856151a6cde64ff55d6444 However I couldn’t pinpoint the exact culprit, so please have a look and let me know if I should look further.