Start Windows in safe mode with networking enabled - https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode

Still In Windows safe mode, start Thunderbird in Troubleshoot Mode - https://support.mozilla.org/en-US/kb/troubleshoot-mode-thunderbird

Does problem go away?

Hi Wayne, thanks for the help. Starting in Troubleshoot mode while in Windows safe mode improved the problem, however I am still experiencing sporadic and long freezes when I do actions in the app such as open mail.

I also experienced extreme performance degradation after upgrading to 128. Deleting a mail or feed item in a folder with 3-10 items freezes Thunderbird for 2 seconds. Deleting a feed item in an RSS folder with 900 items freezes Thunderbird for 30 seconds. Similar size-dependent delay when opening folders. Thunderbird troubleshoot mode seems to reduce the delay by 0-70% (which still means >10s delay for big folders!), but I'm getting very high variance so can't say for sure before more investigation.

@gallium: By chance, does your Thunderbird open a very big mail folder immediately when starting?

see https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems

@gallium: By chance, does your Thunderbird open a very big mail folder immediately when starting?

The folder Thunderbird opens into has about 3000 messages, which seems not unreasonable to me. Other mail apps I use open into folders of 4000 messages.

see https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems

I will try these options if the app becomes unusable again, thank you.

It turned out that my issue was 57k mailnews.tags.* entries in prefs.js. I had the option "Automatically create tags from feed category names" turned on in my news feed and it had accumulated a lot of tags over time, saving a config preference for each. After editing prefs.js directly and removing all mailnews.tags.* lines, there are no freezes when opening folders or deleting items.

And to clarify, this worked fine before version 128, so I'd consider it a regression (though some may consider it https://xkcd.com/1172/), but one easily worked around. :)

Thanks for the update.

Are you using Cards View?

@Wayne: Yes, I am and was using Cards View. I tested that the freezes occurred with and without the Message Pane, but didn't test if Table View had any effect.

Given that https://bugzilla.mozilla.org/show_bug.cgi?id=1342054 is a very old bug report, I don't see why you would not have experienced this problem prior to version 128. Some questions: 1. How long have you been using feeds 2. When did you enable tags? 3. Why did you enable tags, and did you actually end up using the tags

Given that https://bugzilla.mozilla.org/show_bug.cgi?id=1342054 is a very old bug report, I don't see why you would not have experienced this problem prior to version 128. Some questions: 1. How long have you been using feeds 2. When did you enable tags? 3. Why did you enable tags, and did you actually end up using the tags

honvmpri ??