Is it permissible for a Muslim woman to marry a Muslim man in the mosque, knowing that she has not been officially divorced from her non-Muslim foreign husband, who has no religion?

It is not permissible for a Muslim woman to marry a non-Muslim man. Such a marriage is invalid by consensus (ijma') and is considered fornication (zina). If this act was committed with knowledge of its prohibition, then it is a grave sin that necessitates repentance. The children born from such a union are attributed to him if he believed this marriage to be lawful. You are permitted to marry another man without waiting for a formal divorce, as there is no marital bond between you two in sharia (definition). However, marrying another while the civil contract remains might lead to legal problems; therefore, it is advisable to wait until the civil marriage is legally terminated. One must consult scholars about religious matters to avoid falling into such errors. Furthermore, residing in non-Muslim countries entails risks and should be avoided unless absolutely necessary.