I use a KDE Window Rule to force no titlebar. Perhaps your desktop manager has a similar facility. There is an add-on but I couldn't get it to work even though I installed and executed the script from github. https://addons.mozilla.org/en-US/firefox/addon/hide-the-titlebar/

it appeared and disappeared again with no reason

What "appeared and disappeared again"? If you mean the titlebar, isn't that what you want?

What "appeared and disappeared again"? If you mean the titlebar, isn't that what you want?

i was talking about the titlebar checkbox i dont want the title bar the checkbox was supposed to be on the bottom left corner but now it isnt and when there is no checkbox the title bar appears (i dont want it)

In that case, it seems either you need a new profile or you should reinstall. I still have the 'checkbox' but it no longer works for me.

Are you possibly using a window manager that have the title bar disabled ?

Are you possibly using a window manager that have the title bar disabled ?

i dont think so, i didnt change anything in the settings

On Linux this is part of client-side-decoration.

You can possibly look at this pref on the about:config page:

• browser.tabs.drawInTitlebar

On Linux this is part of client-side-decoration. You can possibly look at this pref on the about:config page:

• browser.tabs.drawInTitlebar

changed it to false and nothing happened