This is probably an easy one but, it keeps happening and I don't know how to fix it.
My windows have no frame on certain apps like Firefox, maximised and I can't see any buttons to restore window size to normal. Mahjong starts small window as normal but, no frame nor buttons.
Other programs are doing the same but, some have a close 'x' in the right-hand corner but, not on any frame...
Ideas please - I presume something has happened to a Window or Theme manager.