Additional info regarding 1: Yesterday every row (in panel or mail list) at the mouse pointer was highlighted Today the behaviour has changed, and hovering only will not highlight, BUT unread emails (and only them) will be blanked out as in the attached pictures. Something seems to be really unstable with this "highlight while hover" function....

What operating system are you using Thunderbird on? Very important. From the looks of the images it is not windows 10, or an apple product. It is a long time since I saw 3d boxes like that. The forum reports you posting from a Windows 7 device. Is that the operating system in question?

So you your apparent issues.

1. Thunderbird 78 turns on hardware acceleration in the options. I managed to get it turned off years ago because it was not for everyone. But time has passed and supposedly smarter folk than me think it is ok now. Try turning it off.

Try changing your chosen theme in Windows as well as almost all colours in Thunderbird are actually picked up from that source, although some of the colours and their source is not very intuitive. This highlighting colour does appear to be one of those things

You could follow the advice in this support topic to turn the highlight off. https://support.mozilla.org/en-US/questions/1307570

2. Always a contentious issue with very loud and opinionated folk on both sides. You could follow the advice in this support topic to turn set the row height for yourself to suit you. https://support.mozilla.org/en-US/questions/1307570

3. what you have the windows open in the background waiting for it to update? why not use the notification for when you get new mail and actually open the application when you need to see mail. Having said that, I have two displays with the second dedicated to email and it updates there. Could it just be a windows 7 issue?

4. you could follow the instructions here to use a custom style sheet https://support.mozilla.org/en-US/questions/1309818 or you could just install the Phoenity Icons addon. Go to addons on the menu and type the name into the search box and click install when it is found.

As I wrote: "The issues below is found when running Win7 Pro/64 bit.". I use "classic" theme on this Win7 computer (because of other old SW), and I see no reason why I should not be free to use the Windows standard themes to get TB78 working. Then it's a compatibility problem in TB, not in my head ;-).

Regarding 2 & 3 - I have tried with a userChrome.css file and copied the info in it, but spacing seems to be unchanged. Why ? I don't know....yet. And yes, this modrn "a lot of air and BW" design is splitting people. But with that knowledge - why don't make it (easy) configurable instead of force the change to all users ? Btw the links/references doesn't solve the problem with blank out. The behaviour is also inconsequent from one day to another.

I really do appriciate the answer, do not misunderstand me. But not the solution - it's not ME, as the user, that should reconfigure and change my computer and preferences, download extra add-ons, creating cfg files etc to get the product to work. The product should serve me as the user, not the opposite.

Edit: It was the true/false flag setting that caused settings in userChrome to not work to reduce space, tnx. But hover problem still remains (blank out unread msgs), and - worse - with the now decreased space every mail row "jumps" a little but up and down while moving the mouse pointer...

Did you disable hardware acceleration?

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No. Because I have other programs that needs the HW acceleration.

Instead, I have now spent 4h trying to figure out how to mask the hovering effects, in combination to get a compact mail client, almost looking as before this terrible update was sent out.

Below (in userChrome.css) is what seems to do the work, and in combination to "Phoenity Icons" add-on it looks almost as the TB68, without hover problems and a very compact view:

Perhaps the information can help others:

#folderTree treechildren::-moz-tree-row {
height: 10pt !important;
margin-bottom: -2px !important;
}

#threadTree treechildren::-moz-tree-row {
height: 10pt !important;
margin-bottom: 0px !important;
}

#threadTree > treechildren::-moz-tree-row(selected) {
height: 10pt !important;
margin-bottom: 0px !important;
}

#threadTree > treechildren::-moz-tree-cell-text(hover),
#threadTree > treechildren::-moz-tree-cell-text(unread)
{color:black !important;}

#threadTree > treechildren::-moz-tree-cell-text(selected)
{color:white !important;}

No. Because I have other programs that needs the HW acceleration.

No you don't. The setting is in Thunderbird options and they affect only Thunderbird.

Ok. But as you have seen, the problem is solved in another way without changing such parameters. Probably useful for others.

(And pls delete my duplicate messages, something was strange and they didn't showed up on my computer, that's why I tried many times)

The mouseover issue is recently reported and specific to Windows 7.1. Someone will be looking at it very soon.

I have is issue with mails going white when the mouse hovers over them. Specifically new mails, mails that have been already read don't seem to have this issue.

The problem goes away when the following option is toggled on (Windows 7): Performance information and tools > Adjust Visual Options > Use visual styles on windows and buttons.

Having the ability for users to change the pitch between email lines in options would be a nice feature. Some form of icon customization would indeed be nice.

See https://support.mozilla.org/en-US/questions/1311413 See my reply way down at neilw20 78.4.3 fixed the invisible bug.