Bug 508571

Thanks for the bug report.
I'm not able to reproduce this on Plasma built from git-master with the text in the video, or other text
I also can't reproduce on Fedora 42 with Plasma 6.4.4

Can you share your clipboard settings - General? Thanks

Created attachment 184442 [details]
Clipboard Settings

Created attachment 184443 [details]
Issue on Plasma 6.4.4

A video better showing the issue step-by-step.

Thank you for the screenshot and recording, those are helpful. I have one more question.
I'm still unable to reproduce the bug, with those settings, or with different browsers (one with no addons, ruling out javascript interfering)

Have you seen this bug with any other types of text you try to copy or just with the one website?
Do other websites prevent you from copying text?

I've reported the moment I saw it. Should I try to paste it on Kate to confirm if it's on Plasma's end? Because if I'm able to do that, that wouldn't be on Firefox' end.

I also can't reproduce this issue.

Created attachment 184483 [details]
Issue on Plasma 6.4.4

How odd, I can only paste on Kate if Firefox is open.

I guess this means it's an wayland handling issue.

I hope this doesn't mean that all apps can steal the Clipboard functionality for themselves whenever they feel like it.
That would be a major privacy issue.

In the latest screen recording, the text from a private Firefox window doesn't show up in the clipboard widget, but is able to be pasted into the Firefox URL input
It can also be pasted into Kate
After the private Firefox window is closed, the text can no longer be pasted into Kate

I hadn't realized that the first screen recording involved a private Firefox window, but it also did.
What you're seeing looks intentional. Firefox's private browsing mode is designed to limit the amount of data stored on your computer from the window. Therefore, I confirmed on my system, it behaves as you described. A normal Firefox window allows text to be shared with the clipboard normally.

Can you test and see if you can reproduce this with a normal non-private Firefox window?

(In reply to TraceyC from comment #9)
> In the latest screen recording, the text from a private Firefox window
> doesn't show up in the clipboard widget, but is able to be pasted into the
> Firefox URL input
> It can also be pasted into Kate
> After the private Firefox window is closed, the text can no longer be pasted
> into Kate
> 
> I hadn't realized that the first screen recording involved a private Firefox
> window, but it also did.
> What you're seeing looks intentional. Firefox's private browsing mode is
> designed to limit the amount of data stored on your computer from the
> window. Therefore, I confirmed on my system, it behaves as you described. A
> normal Firefox window allows text to be shared with the clipboard normally.
> 
> Can you test and see if you can reproduce this with a normal non-private
> Firefox window?

It is what is happening. I wish this was something that can be disabled, but I'm marking this bug as INTENTIONAL.

(In reply to TraceyC from comment #9)

> What you're seeing looks intentional. Firefox's private browsing mode is
> designed to limit the amount of data stored on your computer from the
> window. Therefore, I confirmed on my system, it behaves as you described. A
> normal Firefox window allows text to be shared with the clipboard normally.

But this only works in Wayland. If you run Firefox with the MOZ_ENABLE_WAYLAND=0 environment variable, copied items will also be saved to the clipboard history in private browsing mode.

X11 apps can do whatever they want; there is no security whatsoever.

(In reply to Nate Graham from comment #12)
> X11 apps can do whatever they want; there is no security whatsoever.

Hello. I understand the point. But if any feature belongs to Firefox itself, shouldn't it behave the same way when the browser is running in Xwayland mode, or in other desktop environments, and perhaps even in other operating systems?  

I was unable to reproduce the reported issue, and the behavior of clearing the text copied to the clipboard from the clipboard history after closing the browser in the following scenarios:  

In Fedora 42 Workstation Edition (F42-WORK-x86_64-LIVE-20250815.iso https://dl.fedoraproject.org/pub/alt/live-respins) live media, text copied while Firefox 141.0.3 (Wayland) is in private browsing mode can be pasted into a text editor even after the browser is closed. Fedora 42 Workstation, after installing the latest updates following the virtual machine setup, text copied while Firefox 142.0 (Wayland) is in private browsing mode is saved to the clipboard history (gnome-shell-extension-gpaste), and the copied text can be pasted into a text editor after the browser is closed.

In Fedora 42 KDE Plasma Edition (F42-KDE-x86_64-Live-20250815.iso https://dl.fedoraproject.org/pub/alt/live-respins) live media, text copied while Firefox 141.0.3 (Wayland) is in private browsing mode is saved to the clipboard history and can be pasted into a text editor after the browser is closed. I was only able to reproduce the reported issue after updating Firefox version (142.0, Wayland).

Upstream Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1988072

They started marking all data from private windows as a password.

(In reply to y.kde from comment #14)
> Upstream Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1988072
> 
> They started marking all data from private windows as a password.

Thanks for finding and linking the Firefox bug. Since this is an upstream issue that will be addressed by Mozilla, I'm marking this report as such