Title Bar Disappears

If you try going into fullscreen mode and back (F11, or the diagonal arrows icon next to zoom controls in menu), does it appear back?

It might be bug https://bugzilla.mozilla.org/show_bug.cgi?id=2010302 — that however appears to exhibit just on restart IIUC. (See e.g. https://support.mozilla.org/questions/1573272 for more context.)

If you try going into fullscreen mode and back (F11, or the diagonal arrows icon next to zoom controls in menu), does it appear back? It might be bug https://bugzilla.mozilla.org/show_bug.cgi?id=2010302 — that however appears to exhibit just on restart IIUC. (See e.g. https://support.mozilla.org/questions/1573272 for more context.)

I'll do that the next time it occurs and report back. The bar disappears during use, not on launch.

Thank you! Yes, I realize the description sounds different to the existing bug reports, so it's worth watching if this is a separate issue.

BTW in case you're able to access the customization pane in that state, you might want to try Customize Firefox controls, buttons and toolbars and toggling the Title Bar option off/on if it has any effect at that point. (The article also links some troubleshooting steps.)