Firefox : Not possible to get upper case diacritic letters

[wxdf]

If I use Czech or Slovak keyboard, it should be possible after pressing Caps lock to get upper case letters, i.e. if I for instance press "3" I should get "Š".
In Ubuntu 23.10. this works only with Chromium, but not with Firefox(I have Firefox 119.0, but it doesn't work at 118.0,too. So the version of Firefox doesn't matter). If I press Caps Lock, I only get lower case letter "š".
Curiously, this error does not occour under Ubuntu 23.04.
I already asked in a Firefox forum, bur they think, this should'nt be a Firefox problem, but a problem in Ubuntu, I can't say what library or package could be affected.It seems that the programming of Czech and Slovak keyboard contains a mistake.

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Libera.chat.

To change the source package that this bug is filed about visit https://bugs.launchpad.net/ubuntu/+bug/2043900/+editstatus and add the package name in the text box next to the word Package.

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[wxdf (wxdf)]

I've just seen that this isn't a problem only in Firefox, but for instance also in a terminal or in Libre Office, where I can't get upper case diacritic letters like ŠČŘÝŤ after activation of Caps lock.
Why this works under Ubuntu 23.10. only in Chromium, is a riddle, and I don't know what could be the reason.