try restar5ting in troubleshoot mode from the help menu. Continue when prompted and see if it works there. A faulty addon is the most likely issue.

Thanks Matt but didn't help.

Thinking might be bc I'm using such an old version of windows coupled with a recent update?

Maybe I should roll back from version 91.3.0 (32-bit) to 90.x.x?

Tried rolling back to a previous version but discovered that anything prior to v93 (the one I was using when the issue began) gives the warning that my profile is not compatible with this version of Thunderbird. Wants me to start a new profile.

Any ideas out there?

PS I uninstalled all add ons.

see the end of my blog post. I don't think 93 is all that different as yet, but the further from the 91 release date we get, the more likely something will change and not be present when downgraded.

https://thunderbirdtweaks.blogspot.com/2019/09/i-lost-my-profilemail-on-update-to.html

The very same problem started on my TB about when update 91.3.1 (from version 91.3.0) was installed on Nov/16. Quick Filter is misbehaving in the following ways:

1. Neither the toolbar button "Quick Filter" nor "Menu View/Toolbars/Quick Filter Bar" changes the appearance of the toolbar at runtime. The button state (highlighted or not) and menu entry (check mark) changes but the Quick Filter Bar either stays visible or hidden - whatever the Quick Filter Bar started when launching TB. Relaunching TB correctly starts with the state having set (but actually not having visibly changed) before stopping TB. I need to restart TB to get it back or hide it.

2. All criteria buttons in the Quick Filter are working as expected in the current folder (Unread/Starred/Contact/Tags/Attachment), but the free text search is non-functional. It neither starts searching while typing nor opens the additional line to select where to search. Also the pinning does not work. Moving to a new folder does not apply the pressed criteria buttons to it. I have to switch off and switch on again.

I tried a lot already, the Troubleshoot Mode (all combinations of Disable all add-ons/Reset toolbars and controls, Make changes and Restart/Continue in Troubleshoot Mode), update to 91.3.2, change from 32-bit to 64-bit, but in none of the settings and versions the Quick Filter Bar was working correctly again.

New behavior/finding after some more tests: the "Quick Filter" button in the toolbar seems out of sync to the menu entry. And only the menu entry is having an effect on whether the Quick Filter Bar is shown at the next TB start. Furthermore when the button in the toolbar is different to the menu entry and TB is restarted the button reacts only after the second click. As if in the background the button already knew with the first click there would have been no state change and therefore the button can keep it's presentation.

I am really desperate as I used the Quick Filter search a lot my day. I am happy to fill a bug report when you think this is one independent to may personal settings.

I had one more idea to test at which level the error is and created a new profile. Quick Filter is working as expected. So the error must have happened to the profile during the update and seems not reversible. Any idea how to manually fix this editing the profile on disk?

I just encountered the same problem, after upgrade to Thunderbird 91 Windows 10 - Quick Filter not working at all. Very frustrating, eventually after hours of trying troubleshooting, reindexing etc. I went to "inbox," in folder pane, right clicked and chose "open in new window" closed original window and quick filter now seems to work. Fingers crossed

Michael447, you saved my day, my month, my 2021. First Xmas present opened early. This also solved it for me! Thanks so much!

That also solved this exact problem for me after months suffering without quick filter. Now solved, thank you Michael447.

I came pretty close to a long tedious "solution" of migrating to a new profile as suggested on this closed thread https://support.mozilla.org/en-US/que.../1329820 about the same quickfilter broken bug. Be good if an admin could add a pointer here to a real solution.

By chance I revisited the discussion at https://superuser.com/questions/856009/thunderbird-quick-filter-suddenly-stopped-working which I did not read to its end because I thought is a different issue. But actually https://superuser.com/a/1577880/813859 already contained the same solution as for this issue.

I just encountered the same problem, after upgrade to Thunderbird 91 Windows 10 - Quick Filter not working at all. Very frustrating, eventually after hours of trying troubleshooting, reindexing etc. I went to "inbox," in folder pane, right clicked and chose "open in new window" closed original window and quick filter now seems to work. Fingers crossed

Thanks Michael447.

This seems to be a recurring issue. I spent some hours trying to test and find the reason for the issue and was contemplating creating a new profile and migrating all of my emails to the new profile ... quite a daunting task and could lead to the risk of creating even more issues.

MIchael447's fix worked and is simple.

Marc Mageia8 Linux, Plasma 5.20.4