There is a forum post about it https://forum.joomla.org/viewtopic.php?f=839&t=1015710, figured here on GitHub is more likely devs would use GNU/Linux.

I'm sorry but I can't replicate the issue with Firefox 137.0.2 (64-Bit) on Debian 12 Bookworm. can you test with uptodate firefox please?

Can you test with ESR :) ? I am sorry but it is up to date, except it is the ESR, the long term support version, included by default in the OS https://support.mozilla.org/en-US/kb/switch-to-firefox-extended-support-release-esr and the version is the latest, even the installer for Windows is called Firefox Setup 128.9.0esr.exe. That's what almost all the corporations are using, the ESR. Nevermind some derivatives that try to keep Mozilla out of the user data.

Of course I will test with the version suggested but right now from here the repo seems down, will try again today. But only in the interest of "science".

Sorry - ESR versions are not deprecated or something, and Joomla should surely run smoothly on those.

I installed it via Flatpak and I have Firefox 137.0.2 (64-bit).

I can confirm that in this version there is no problem, on the Dashboard the modal for adding modules opens and stays properly opened, and selection is working,

@Fedik can you have a look Please?

Works fine for me on Firefox 137, I cannot check on older.

However, there were no any changes since Joomla 5.1 for the dialog script, and I have no idea what went wrong with Firefox 128 and Joomla 5.3.

Firefox 128 on windows (tested with browserstack) has no problems

I had this same issue and it was driving me mad.
Then I went into Chrome (also had the same issue with Firefox) and switched all my chrome extensions off and then on again one by one as with all off and in incognito mode, it suddenly worked. As I switched them back on I got to BitWarden... and it stopped working again.
So I contacted bitwarden support and they said opps can you switch off the setting that automatically appends to the field and when I did, it worked, so they said they would fix the issue in the extension which they did for the next update, but broke it again recenlty.

So try stitching off all your extensions in chrome of firefox and try incognito and see if that fixes the "joomla" issue

Cannot replicate on ff latest version and others on my PC (win11).
Could you check your console, if there are error-messages?

No errors in the console unfortunately.

I am astounded that this can't be confirmed: it happens on 2 different machines, both on my desktop and my laptop that don't have any problems whatsoever, in 2 different browsers - across Firefox and the fork Floorp. Both machines running Debian Bookworm fully updated.

Installed Floorp now just for you, but cannot replicate the issue. (win11)

For now this seems to happen only on Debian

... So I contacted bitwarden support and they said opps can you switch off the setting that automatically appends to the field and when I did, it worked, so they said they would fix the issue in the extension which they did for the next update, but broke it again recenlty.

So try stitching off all your extensions in chrome of firefox and try incognito and see if that fixes the "joomla" issue

OMFG that was it! I disabled uBlock Origin, Privacy Badger and the likes, that sometimes interfere with things - but never encountered such a problem with Bitwarden, and of course I needed it for logins. So it didn't occur to me.

As soon as the extension was disabled, the modals were fine.

Thank you all for your time and I am going to pest the Bitwarden dudes. Though... why is only Joomla? And why only the modal for adding modules from the Dashboard?

Anyways this is solved. Thank you @flo-the-cat !

Thanks for the info. So I close this - no Joomla issue.