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• Firefox frequently crashes for no apparent reason. Even when I don’t open any websites and just leave it idle, it crashes on its own after 4–5 minutes.

The crashes happen on all websites, not just specific ones.

• When I reopen Firefox after a crash, sync is completely unresponsive and shows “Paused.” It takes another 30 seconds to a minute before it starts working normally again.

• Every time I open Settings, Firefox becomes incredibly laggy—like a game running at 20 FPS—to the point where it’s barely usable.

• I’ve tried clearing the browsing data, but nothing has changed. Do I really have to uninstall Firefox and reinstall it?

• I’ve temporarily switched to Brave over the past few days. Firefox’s testing team has done a really poor job this time.

P.S. I’m using iOS 18 on an iPhone 11.

Thunderbird has become extreme slow. Like it's doing task in the background. Takes emails longer to display and mouse becomes jerky. All other programs OK Especially noticeable after leaving TB running for a while. The previous versions were snappy. This version is very noticeably slower.

My Thunderbird (158 Meadow) is very slow sending emails. Up to 30 seconds for an ordinary message. Most often thew people are in my address book but even if they are no the problem is common across all outgoing emails. Windows 11 Laptop 26H2, 64Gb Ram, 500Gb SSD, 200GB free, i7 (12 Edition) Intel I have already checked that my Windows Defender antivirus has the profile folder as an "exception" Compressed my "send" folder Run "repair" on my send folder I have about 500 emails in my send folder I have an IMAP set up with SMTP set to 465 SSL/TLS Normal password I have checked my webmail and that works fine so it is not a problem with hosting etc.

After Firefox & Thunderbird update & Windows (11) update, it takes ages for the email programs to open and the web pages to open. Tried everything, to no avail. Any ideas apart from uninstalling and starting again? The imap lookup takes ages and when opening website pages it takes ages. Googles is very quick to open.

I was referred here from Thunderbird Bugzilla report 2081665.

We are experiencing a recurring problem with Thunderbird 153 on several Windows workstations in a business environment.

The important point is that the problem also occurs with completely new Thunderbird profiles created from scratch. It is not limited to migrated or old profiles.

On one workstation this has already happened to three separate Thunderbird profiles.

Typical sequence:

1. Thunderbird 153 is installed. 2. A completely new profile is created. 3. Mail accounts are configured manually. 4. Everything initially works normally. 5. After some time the profile begins to malfunction. 6. Thunderbird Settings no longer open/respond. 7. The address books still exist, but address autocomplete when composing a new message stops working. 8. Creating another new profile temporarily fixes the problem, but the same behavior can return later.

Troubleshooting already performed:

- Troubleshoot Mode - extensions disabled - tested without the existing prefs.js - rebuilt Thunderbird caches and profile UI state - recreated indexes/databases - completely removed Thunderbird from Program Files, AppData\Roaming and AppData\Local - clean Thunderbird installation - clean profile created from scratch - Thunderbird executable and profile paths added to Kaspersky Endpoint Security trusted applications/exclusions

Removing prefs.js from an already affected profile did not restore the Settings window.

A clean test profile initially works correctly.

We have also encountered this behavior on other workstations. Some users have more than 100 message filters and many folders, so rebuilding profiles repeatedly causes significant administrative work.

Several affected computers had Windows user accounts renamed in the past.

We also experienced a separate issue where the Attach File dialog stopped appearing while drag-and-drop still worked. Bugzilla identified this as the already known Bug 2077590, so I consider that a separate issue.

For comparison, after completely cleaning Thunderbird from an affected workstation and installing Thunderbird 115.3.1 with a clean profile, the same workstation currently works normally.

Because freshly created Thunderbird 153 profiles can later develop the same problem again, simply recreating the profile does not appear to be a permanent solution.

Environment:

- Windows workstations - Thunderbird 153 ESR - Kaspersky Endpoint Security - multiple IMAP accounts - business environment

What diagnostic information should I collect from the next affected profile before replacing it?

I can provide:

- Thunderbird Troubleshooting Information - Error Console output - profile file names/sizes/timestamps - Windows Event Viewer logs - sanitized prefs.js - comparison with a working fresh profile

Bugzilla report: 2081665 Known separate attachment bug: 2077590

Hello, I am having an issue that Emails which are displayed in the reading area disapper for appr. 2 minutes. Afterwards they appear again. I have not been able to find out if this is a problem in Thunderbird, or if another application is causing this. I have read an article that Avast Antivirus is temporarily locking folders during scan. Maybe someone has had the same topic and can give me a hint where to search for the root cause. Thank you.

My Thunderbird connected to my gmail is running slow. Thunderbird is not running slow on my other (non-gmail) account. It takes 10-15 seconds for an e-mail (from gmail) to be deleted or moved within Thunderbird. I have tried "compacting folders" and "repairing folders" and that does not help. Please help!

I am having constant problems for months now with Thunderbird freezing and message not responding. It appears to happen mostly when trying to empty deleted folder in block like 20 or more. If I deleted in blocks of four all is ok. As soon as I try to delete a larger amount at once it freezes and displays the message Thunderbird Not Responding. I have followed u tube videos to the letter to attempt repair with no success any ideas please?

This happened once before - then cleared after the next update. Now, after a recent update, the browser display is unstable again. Not a problem with any other browser - so it's NOT the computer. Any suggestions ?

Thanx, Dennis

I upgraded my system to Kubuntu 26.04 LTS and started Thunderbird. The window where messages are listed was covered with Thundrbird presentation asking for donation. Only edge of one message is seen above the presentation and I cannot get to the list

Hi,

I'm having a performance issue with Firefox on my computer. After Firefox has been running for a while, it sometimes becomes noticeably slower when I use several browser-based tools and keep multiple tabs open.

For example, I noticed it while using an online one rep max calculator to work out estimated lifting numbers. The calculator itself is fairly simple, but Firefox occasionally starts using more CPU and the browser feels less responsive.

I have several extensions installed, so I'm not sure whether an extension, a particular tab, or Firefox itself is responsible.

I've already tried closing unnecessary tabs, but the problem can still come back.

Is there a good way to determine whether a Firefox extension is causing the high CPU usage? Would checking about:processes or running Firefox in Troubleshoot Mode be the best way to narrow it down?

I'm especially interested in knowing how to identify the specific extension or tab responsible rather than disabling everything permanently.

Thanks.

Hello, so. I just moved from Chrome to Firefox recently. My first move was on my laptop which I enjoyed the experience so I had to try out the mobile version. So far the experience has been pretty okay but I have been coming across occasional crashes and the app is sometimes slow generally. I tried figuring out what's going on by googling how to make the app run faster. I deleted all my mobile extensions but the difference wasn't too visible. I still do experience some last when accessing memory hungry website's like Instagram and Facebook. I know I can just have the apps but I prefer to use the website's (it helps me reduce my doom scroll period). But if I'm being fully honest, I think it's because of my phone in general. My phone is a Samsung A16. The phone on it's own has been generally slow so I think that might be the case but I can't say for sure because the frequency of the app freezes and lack in speed wasn't as common when I was using Chrome. By no way am I saying Chrome is better but I'm just saying that Chrome was faster than Firefox. I'm mostly facing these problems on my phone. Who knows maybe it's my phone still getting used to the app. I really want Firefox to work because it's been a good experience overally plus the added privacy and VPN are a great bonus I never knew I needed till now. Anyways I hope this is just my phone being moody and not the app, I am planning on upgrading the phone soon anyways so I hope that will change. But yeah I just wanted to let you know that this is what I'm experiencing, otherwise everything else has been great. I hope someone can help me out.

Have a great day.

I'm on a 15" MacBook Air M5 running and updated OS to Golden Gate 27.0 a couple of days ago. when I Open Thunderbird the emails are up but page is blank, just spinning pizza wheel. I've force quit Thunderbird and restarted and force quit and shut down several times but ends up with the same result... just the spinning wheel. Any suggestions ?

I'm running Thunderbird 156.0 on Windows 11 with ten IMAP accounts (Gmail, Outlook.com and Zoho) plus one Exchange account served by the Owl add-on, and until recently about 30 GB of mail held locally. On starting Thunderbird, folders are destroyed and re-created empty. It happens often, but not every time. The summary files are deleted, and in some cases the whole folder directory goes with its mbox message store inside it. The folders then come back in the folder pane holding nothing, and Thunderbird downloads all the mail again over several hours, re-indexing as it goes. When a folder directory has been re-created, it appears on disk with a numeric suffix, so one of my folders now lives at COMPLIANCE-1.sbd with an abandoned COMPLIANCE-2.sbd sitting beside it. Column layouts and favourite-folder flags are lost at the same time, because they live in the summary files. It happens on ordinary restarts, rather than after Windows updates or sleep.

Those orphaned directories have let me date three separate occurrences: 18 August 2025, 19 February 2026 and 19 September 2026 — those being the occasions that happened to leave orphaned directories behind. Most leave no trace, because the folder refills and the evidence is overwritten. Each has the same signature. A folder directory is created, and roughly five minutes later a summary file of about 1,200 to 1,500 bytes, which is an empty summary, is written into it. In the two older cases it was never touched again. In one event eleven summary files across two folder trees were written with an identical timestamp to the second, so it appears to be a single operation across a set of folders rather than something that walks through them one at a time. One of the destroyed folders left its mbox stores behind, orphaned with no summary file, while another was deleted whole with 50 MB of mail inside it, so there seem to be two different outcomes in the same event. Bitdefender is running, but its quarantine holds nothing from the September event, and there are no Thunderbird entries in the Windows event log for that period.

The part that may be useful is that I have reproduced it. On 19 September I renamed folderCache.json aside with Thunderbird closed and restarted. Eight minutes later folders were destroyed. The twelve I could identify were all children of INBOX, across two different mail providers, though other folders elsewhere were emptied in the same minute. The Exchange account served by the Owl add-on was untouched. At the moment of destruction the Activity Manager showed "[NONEXISTENT] Invalid folder: INBOX^Practice Filing (Failure)" on the Gmail account, where the correct hierarchy delimiter is a forward slash rather than a caret. My folderCache.json is 5.2 MB with about 13,000 entries, of which roughly 1,200 point at summary files that no longer exist and 9,600 sit under an obsolete lowercase profile path from the 129 to 139 version window. I would rather not delete it again given what happened, so I'm looking for any idea of what triggers this on an ordinary restart, and whether there is anything I can set that would stop Thunderbird discarding local folders when it decides they are missing.

I am going in circles with this. If I build a new profile, is there any point bringing the old configuration across, or would that just reimport whatever is wrong? I assume the address books and filter files are safe and that folderCache.json, prefs.js and the unified-folders directories are not, but I do not know whether the problem lives in the profile at all, or in how Thunderbird handles an account set this size.

Any ideas?

Firefox runs real slow when I changed screens. Sometimes many seconds, things just quit working screen goes blank.

Sometimes it goes to wrong screen. I do not know how to reinstall or update. I would like to talk to a person I am old. I have no technical ability at all. I am confused by all instructions online. Please help me