Check : Do you have this setting ?

• Settings > General
• scroll to 'Reading & Display'
• Select 'Automatically mark messages as read'
• select 'Immediately on display'

See if this is due to an index file being squiffy.

• Right click on folder and select 'Properties'
• click on 'Repair Folder'
• Click on OK
• Select a different folder and reselect Inbox.

If still no joy: Please restart Thunderbird in Troubleshoot Mode In Thunderbird

• Help > Troubleshoot Mode
• click on 'Restart'
• Select 'Continue in Troublshoot Mode'

If it works ok then the issue maybe an addon or perhaps hardware acceleration.

What addon extensions have you installed ? If none then try this:

• Settings > General
• Scroll to bottom
• uncheck 'Use hardware acceleration when available'

Please report on results.

Thanks for the replies. I had already tried Automatically mark messages as read...Immediately on display AND Repair Folder (on several folders).

In Troubleshoot Mode, I tried these one at a time: 1) I disabled my one add-on. 2) Then reset toolbars and controls. Unchecked Use hardware acceleration when available

None of this changed anything. My mail list pane text is still all BOLDED (see image) and does not change when I use the Mark button.

Are these emails in a Unified Inbox ? meaning do you use 'View > Folders > Unified' ?

Or they are in an accounts own Inbox ?

Did you try: Right click on folder and select 'Mark folder read'

Folders View = ALL (tried other views, no change) Did try Mark Folder Read

re In Troubleshoot Mode,

In Troubleshoot Mode, I tried these one at a time: 1) I disabled my one add-on. 2) Then reset toolbars and controls. Unchecked Use hardware acceleration when available

Not sure whether you did the option requested. The info you supplied sounds like you were selecting the Troubleshoot mode checkboxes.

Did you do this option.

• Help > Troubleshoot Mode
• click on 'Restart'
• do not select any checkboxes
• Select 'Continue in Troublshoot Mode'

This option would have disabled everything anyway, so knowing the outcome would be good.

You said "1) I disabled my one add-on." What is the name of the addon you have installed ? Please note just disabling that addon may not have completely switched off everything. You would have needed to uninstall it and then restart Thunderbird.

OK. I restarted in Troubleshoot mode without checking any boxes. Still bold text.

I have 2 Add-ons: EditEmailSubject MX & Bitdefender Toolbar I uninstalled the first one, disabled Bitdefender, but it cannot be uninstalled...it does come back on after restart. Still have bold text.

I tried something else: Settings > General > Language & Appearance > Fonts & Colors: changed it to a weird Default Font and nothing changed in the mail panel. Is the text in that panel not controlled by this setting?

Also changed the font under Composition and that did work.

re :Bitdefender Toolbar

Judging by the comments it sounds like a real pain in the proverbial. This discussion has a method of dealing with that Bitdefender Toolbar.

• https://community.bitdefender.com/en/discussion/93701/remove-anti-spam-toolbar-in-thunderbird

tihabil says: -Tb must be closed -go to the extension folder "...\profile\extension" -copy the name of extension file including its filename extension '"bdThunderbird78@bitdefender.com.xpi" and then delete the extension file. -create a folder or a text file wit no information and rename it with the name of extension file you have. For me, now the file name is "bdThunderbird78@bitdefender.com.xpi" -right-click on it and change NTFS permission there will be 4 groups of users. You must deny permissions to 2 of them: -"Authenticades Users", "Administrators" . DO NOT TOUCH "SYSTEM" permissiones.

After this last step, no BD Anti-Spam Toolbar wil be installed/reinstalled...until Bitdefender wil be upgraded and probably change the name of extension. If this will happend must repet these 4 steps using the new name of extension-file.

Easy way to locate the necessary file: In Thunderbird

• Help > TRoubleshooting Information
• Under 'Applications Basics' - half way - profile folder - click on 'Open Folder'

A new window opens showing you the contents of your profile name folder.

• Exit Thunderbird now.
• Click on folder called 'extensions' to see list.
• locate the file that ends with "....@bitdefender.com.xpi"
• Move it to desktop and then get a copy of it's filename including extension.
• Create a new text file document - it can stay empty - give it same filename as the one you moved to desktop.
• save in 'extensions' folder thus replacing the one you moved.
• Then right click on file and change the permissions as advised by tihabil
• Finally delete the file you moved to desktop.

I did all that and the Bitdefender add-on does not appear in Thunderbird. Still have bold text. Also restarted in Troubleshoot mode.

Here's another thing: When I look at the mail panel in CARDS view the Mark button appears to work. It does not work when in TABLE view. Could that be a clue? Maybe it's a vs. 115 issue? See image of Unread & Read in Cards view.

I solved my problem. I had installed a System Font Size Changer awhile ago and had everything set to Bold. This did not affect Thunderbird vs. 102, but evidently is a problem in vs. 115. After removing Bold on one setting, I can now see which emails have not been read. Plus the Mark button works now. Thanks for all your help.