Created attachment 7648 [details]
screenshot

I have found the culprit but not sure how to deal with it.

The effect is not there in a new user.

Re-naming the file .gtkrc-2.0-kde in my own user cures the problem, but I am not sure what else this may break.

The file contains:
#---------------------------------------------

# File created by KDE Gtk Config
# Configs for GTK2 programs 

include "/usr/share/themes/oxygen-gtk/gtk-2.0/gtkrc"
style "user-font" 
{
	font_name="Sans Serif "
}
widget_class "*" style "user-font"
gtk-font-name="Sans Serif  9"
gtk-theme-name="oxygen-gtk"
gtk-icon-theme-name="oxygen"
gtk-fallback-icon-theme="hicolor"
gtk-toolbar-style=GTK_TOOLBAR_ICONS
gtk-menu-images=0
gtk-button-images=0

#-------------------------------------------

I use the same /home/me folder for Mga5 and Mga6 and it was used previously for earlier versions.

(In reply to Barry Jackson from comment #2)
> I have found the culprit but not sure how to deal with it.
> 
> The effect is not there in a new user.
> 
> Re-naming the file .gtkrc-2.0-kde in my own user cures the problem, but I am
> not sure what else this may break.
> 

Thanks,  Barry. I have the issue, too, also using an "old" /home, but kept forgetting to check whether the issue exists only in Plasma5, or in XFCE (my fallback), too... so I kept postponing to file a bug report. I hadn't thought of testing with a new user.

I don't have a .gtkrc-2.0-kde, though, but do have 2 gtkrc-2.0 files

[marja@cldrn_64 ~]$ find | grep gtkrc-2.0
./.kde4/share/config/gtkrc-2.0
./.config/gtkrc-2.0
[marja@cldrn_64 ~]$ 

At the top of those files it says:

# If you do not want KDE to override your GTK settings, select
# Appearance -> Colors in the System Settings and disable the checkbox
# "Apply colors to non-KDE4 applications"

That checkbox did not exist, but there was a similar checkbox for applying colors to non-Qt applications. Unchecking it fixed the problem for me: the tooltip texts are white on black now

Summary: thunderbird tooltips are black on black => thunderbird tooltips are black on black, unless .gtkrc-2.0-kde gets renamed or applying colors to non-Qt applications gets disabled
Source RPM: (none) => thunderbird-38.7.2-1.mga6
CC: (none) => doktor5000, marja11
Assignee: bugsquad => mageia

is it still valid with current cauldron ?

CC: (none) => mageia

Can't easily test now as I run thunderbird over ssh on a Mga5 server.
I suppose it would require a working Thunderbird install on Mga5 updated to Mga6 to test and I won't be updating my server any time soon ;)

Can't reproduce this inside M7, Cauldron and even a M7 32 bits on a VM. 

We are sorry, but we no longer maintains this version of Mageia. Please upgrade to the latest version and reopen this bug against that version if this bug exists there.
As a result we are setting this bug to RESOLVED:OLD

Resolution: (none) => OLD
Status: NEW => RESOLVED
CC: (none) => ouaurelien