The default is off. The settings for this are stored is a session.json file in the profile folder and historically most folk who have issues with the toolbar reverting to default also have ccleaner deleting the storage file "for your security" or some such.

I don't use Ccleaner. That the default is "OFF" is irrelevant! I set it to ON, and for whatever reason, Thunderbird flips it at random. That's a bug, and it needs fixing!

(ps 25 years in IT, I know what I'm talking about ;-> )

Cheers Jeremy

Just because it randomly switches off does not necessarilly mean it's a bug. If it were a bug usually it means several people would be reporting the problem and no other reason was effecting the cause. That is not occuring.

Matt's info is really useful. It's not just CCleaner or other similar products like WiseCleaner that can cause an issue with a session file, there are plenty of Anti-Virus products that can also cause a problem if they are allowed to scan profile folders or clean up session files. I've often come across this as a problem.

Another reason for it occuring: I have come across people who report same issue -Quick Filter Bar keeps randomly switching off - only to discover they were unknowingly switching it off. This is usually more likely to occur if you are someone who is familiar with using the keyboard which I'm assuming you may do since you've been in IT for a while.

• The keyboard 'Esc' key is the shortcut to switch it off.
• The keyboard 'Shift'+ 'Ctrl' + 'K' will switch it on.

Is it possible you have unknowingly been using the shortcut key that auto switches it off ?

It would help if you tell us how you switch it on. As you may be aware, there are various methods designed to suit personal needs. Then we can check to see if the method you use has been reported as having a problem. Do you normally use the keyboard or mouse click method ? Do you use the 'Quick Filter' button on the 'Mail Toolbar' to enable/disable the Quick Filter Bar ? Do you use the shortcut keys as mentioned above? Do you use the 'Menu Bar' toolbar ? - eg: 'Alt' + V then T and then Q ? Do you use the 'Menu icon' the 'View' > 'Toolbars' > select 'Quick Filter Bar' ?

What OS are you using ? What version of Thunderbird are you using ?

Windows 10 x64 ALWAYS up to date

Thunderbird 102.11.0 (64 bit)

I use Windows Defender and Malwarebytes, which runs daily.

Sometimes I have the Quick Filter toolbar for days, then it disappears more than once.

Nothing should change it except ME. 25 years in IT.

This is a bug. It shouldn't happen.

Please provide responses to all the other information I asked. I'm not sitting next to you and I'm not a mind reader, so I do not know what processes you use.

I'm not sure what level or experience you have in all the various areas that IT can mean or what you have been involved with for all I know you could have just been using MS Office but either way I'm sure you understand why the information is required.

I agree, it should be only you who chooses what occurs, but at this point, it's possible it is you or the computer AV etc. That's why we need information.

You mention you are using Windows Defender and Malwarebytes. Are you saying you allow your thunderbird profile folders and all files therein to get scanned by these products ? Have you got them set up to auto fix files or just quarrantine them or ask you what to do with files these products do not like ? Never allow these products to auto fix any thunderbird file or folder, always force it to ask what to do. If it is set to quantine then is anything in the quarrantine folder?

OR Is your Thunderbird profile folder exempt from allowing any scanning access by Windows Defender and Malwarebytes ?

Basically, it sounds like you have stated - you are running software that can remove suspicious files, temporary files, session files etc and you are allowing them access to files in the Thunderbird profile.

If this is true then make the Thunderbird profile folders exempt from access by both Defender and Malwarebytes. You have to be certain these programs are not messing around in Thunderbird.

Malwarebytes warns me of any item quarantined.

Software specialist working on high end academic library catalogues - special software on top of our packages. For customers such as Oxford University, Trinity College Dublin and the National Library of Wales. Hacked my first code in 1967. Worked with our OS and Comms specialists in Canada on interfaces to our systems, including debugging low level interfaces.

Malwarebytes now told to ignore Thunderbird folders. Windows Defender does not offer this, as it knows Malwarebytes is my main AV software.

QF toolbar fine this morning. Will let you know if it stays that waty.