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On my Windows 11 PC, when I open my Thunderbird Address Book and click on any entry, or right-click and select any option, a solid grey veneer overlays the Address Book window, and nothing else happens: The feature hangs. I can close the window and continue to use Thunderbird, but all I can do in the Address Book is scroll through the names and email addresses. When this first happened, I updated Thunderbird to release 159.0 (64-bit), but the same thing happens in that version. I've done web and forum searches and have not seen any other reports of this. Any ideas as to why this is happening to me, or how I might fix it? (I've attached a redacted screen image showing what I see.)

ive just downloaded firefox and its giving me performance issues I play gta 5 all day with my chrome tabs open maybe more then 5 sometimes more then 8 and When I had more then 4 or 5 tabs my gta 5 started to lag when i opened my task manager i see that Firefox is using more then my Game.

Hey,

I have this visual bug on Firefox where spaces on my screen get blurred, flicker or are just another color than they're supposed to be. This happens on every website and even on the menu bar or when I hover over bookmarks. It's hard to describe, so I attached some screenshots.

I've already tried: Restarting the laptop, restarting Firefox, opened Firefox as admin, cleaned Firefox and went to "about:support" and gone into the troubleshooting mode. When I'm in troubleshooting mode, the bug disappears but as soon as I restart Firefox, it's there again.

Sometimes the bug changes when I scroll or move my cursor, as you can see on the two screenshots from Twitter (X). Sometimes it's barely noticable, like on the PDF website and sometimes I can't even read text fields as in the chess.com screenshot...

I am using YouTube. One singular tab of YouTube takes up 4 GB of ram. Two tabs take 8 GB. Having more than two tabs quite literally provides me 20 GB of memory usage. This is preposterous.

The fixes I have tried is

- Disabling all extensions; this does not help in the slightest. - Refreshing the startup cache - helped first 10 minutes went from 400mb to later 5 gb (one tab) - Refreshing the Firefox cache - helped also first 10 min, and then memory leakage came back. - Disabled YouTube Ambience - did not help.

I have a top-end gaming computer, this should not be an issue.

I am not sure what to do from here on out, please advice

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 have noticed that Thunderbird has been very slow and glitchy very recently.

Some messages take ages to load. Sometimes the whole program hangs and becomes unresponsive.

Recently (last week or 2), whenever I delete an email, the unified inbox shows an empty display, but, if I select the three lines and go to inbox and select it, all the expected emails reappear.

My question can suffice. Once I installed Thunderbird release over the Thunderbird ESR, I have very slow or no access to messages sent before my account was converted to Graph. Confirm?

• 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.

recently, e-mails have been hanging. I have determined that it is, for the most part at least, USPS mail tracking e-mails that hang. Once I delete or move to archive, things download fine.

This is not the daily Informed Delivery e-mail.

This is like "your package (tracking number nnnnn) has arrived at the distribution center. Expected delivery mm/dd/yyyy.

I have restarted, repaired in box, etc.

Any help?

When searching for "woolworth sarina". the browser does crash. Same thing happened yesterday when serching for "corona specials mackay"

What is the issue? This never happened before. I reinstalled Firefox Focus and did get the same result.

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.

I am unable to access my emails in Thunderbird. Thunderbird opened but does not respond as there appear to be some files /emails that it could not accessed.

I tried deleting the Parent.lock file. I then deleted Thunderbird and re-installed it.

On opening the updated instance, it comes up with the same couple of files/emails in the list. With the same ones seemingly trying to be loaded. See attachment. The files are Invoice 03-10-20 and Ticket_1.pdf

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.

It's very odd. Normally moving an email, say from the Inbox to the relevant year's archive, takes "no time at all".

Which is true for all the mailboxes shown on the attached screenshot, EXCEPT for the four at the bottom. Moving even one message from Inbox to Yiddish can take ten seconds or longer (with the dreaded "Not Responding" occasionally). Moving something in the opposite direction is also screwy, only from those four.

I had thought that it was because they're rather large. This first started when there were just Yiddish and MSW, and I split off most of the earlier years into the archives shown. To no avail.

It's only an annoyance, but I'm puzzled about how such a thing could happen.

Also very slow tagging or untagging a message just in those mailboxes.

Moderator Notes:

• need a performance profile https://support.mozilla.org/en-US/kb/profiling-thunderbird-performance

Since Firefox 157, each version is stealing more and more RAM. Why? My Windows XI, on HP with an AMD processor, are constantly losing more and RAM to Firefox. Is there any advice? Or must I suspend all updates?

• • Subject: Severe recurring UI freezes after upgrading Thunderbird from v114 to v150+ — application becomes unresponsive after being left idle**

Hello Thunderbird Support Team,

I'm experiencing a serious and persistent performance issue with Thunderbird that began immediately after upgrading from version 114 to version 150 in September 2026. The problem has continued through multiple subsequent updates and is now severely affecting my daily work.

I've been using Thunderbird for years, and it worked reliably before this major upgrade.

• • The problem**

Thunderbird launches normally and initially works perfectly. However, after I leave it open in the background while working in other applications, it frequently becomes completely unresponsive when I return to it.

Specifically:

- Thunderbird is initially fast and responsive after launching. - After approximately 5–10 minutes, or sometimes after a longer period of inactivity, it begins experiencing severe lag or freezes completely. - When I switch back to Thunderbird, the interface is often unresponsive for several minutes. - I often have to force-close the application through Windows because it becomes practically unusable. - Restarting Thunderbird temporarily restores normal performance, but the problem eventually returns, when it's left idle. - The issue occurs repeatedly throughout the day and makes it very difficult to use Thunderbird reliably.

Importantly, this is not simply slow startup performance. Thunderbird initially works perfectly, and the freezing develops after it has been running for a while, particularly when left in the background.

• • Version and environment**

- Operating system: Windows 11 Pro, 64-bit - Thunderbird version before the upgrade: 114 - Version initially upgraded to: 150 - Subsequently confirmed version: 156.0.1 (64-bit), on September 29, 2026 - Problem first appeared: September 2026 - Problem still present: October 22, 2026 - Current Thunderbird version: 158.0.1

• • Troubleshooting already performed**

1. **Global search indexing:** I noticed that Thunderbird's Activity Manager frequently displayed "Indexing messages." I suspected that indexing might be causing the problem.

2. **Disabled Global Search and Indexer (Gloda):** Unfortunately, this made no meaningful difference. Thunderbird continued freezing even with global indexing disabled.

3. **Multiple Thunderbird updates:** The application has been updated repeatedly since the initial upgrade, but the freezing has persisted.

4. **Restarting Thunderbird:** Temporarily resolves the problem, but only until Thunderbird has been running for some time.

• • Additional unusual behavior: Google OAuth authentication**

On at least two occasions, after force-closing an unresponsive Thunderbird process, Google Chrome unexpectedly opened a Google authorization page saying:

"Mozilla Thunderbird Email wants access to your Google Account."

The page also indicated that Thunderbird already had some access to the Google account.

After clicking "Continue," Chrome redirected to a localhost address (127.0.0.1 equivalent, using a dynamically assigned port), which failed with:

"ERR_CONNECTION_REFUSED — localhost refused to connect."

I suspect this happens because Thunderbird is no longer running to receive the OAuth authorization callback.

I'm not sure whether the Google authorization issue is directly related to the freezes, but the repeated timing is suspicious and could indicate a background synchronization or authentication problem.

• • Impact**

I use Thunderbird extensively for professional correspondence and managing my translation business. These recurring freezes are seriously disrupting my workflow.

The problem has now persisted for over a month, despite updates and troubleshooting. It is becoming increasingly difficult to continue using Thunderbird in this condition.

• • What I would appreciate help investigating**

Could you please advise on how to identify the background process or operation that causes Thunderbird to become unresponsive after it has been running for several minutes?

In particular, I would appreciate guidance on:

- Whether this is a known regression affecting users who upgraded from much older Thunderbird versions. - Whether IMAP synchronization, background authentication, or Google OAuth activity could be responsible. - Whether there are diagnostic logs or performance profiles I can collect while Thunderbird is frozen. - Whether a particular database, profile component, or setting could be responsible without requiring me to rebuild my entire Thunderbird setup. - Whether there are known fixes or workarounds.

I'm happy to provide additional diagnostic information, screenshots, or logs if that would help identify the cause.

I would particularly appreciate a way to capture what Thunderbird is actually doing during these freezes, rather than continuing to try speculative troubleshooting steps.

Thank you in advance for your assistance!