Unlikely. Did it say what bug number it is?

It is possible that a website disables the Firefox spell checker by adding a spellcheck="false" attribute to the input field. You can check this in the Inspector via the right-click context menu.

• https://firefox-source-docs.mozilla.org/devtools-user/page_inspector/

If that is the case then you need to enable the spell checker yourself.

Firefox doesn’t spell‑check in Copilot because Copilot uses a modern custom text editor that Firefox doesn’t recognize as a normal typing area. Since Firefox never turns its spell‑checker on in this kind of editor, nothing actually fails, so there’s no error code or message. The spell‑checker engine simply never activates. For this to work, Firefox would need to update its spell‑checker so it can handle newer web‑based editors instead of only traditional text boxes.

Firefox doesn't spell‑check in Copilot because its editor sets spellcheck="false", just like cor-el stated above. Firefox doesn't need to do anything with this, please reach out to Microsoft instead.

I'll mark cor-el's reply as a solution since there doesn't seem to be anything else we can tell you.