Is working for a marketing company that promotes an online stock trading platform, which offers stocks from all companies and banks, both usurious and non-usurious, permissible or impermissible?

The rule concerning products used in both lawful (halal (definition)) and unlawful (haram (definition)) contexts is to refer to the certainty of the purchaser's intent. If it is certain that they will be used for unlawful purposes, then their production or sale is impermissible. If it is certain that they will be used for permissible purposes, then there is no disagreement regarding its permissibility. If the matter is unclear and it is not known whether they will be used for lawful or unlawful purposes, then one should act based on the predominant assumption. If it is predominantly assumed that they will be used for unlawful purposes, their sale is forbidden. If it is predominantly assumed that they will be used for lawful purposes, their sale is permissible. It is not permissible to cooperate in sin and aggression. Allah the Almighty says: (And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allah; indeed, Allah is severe in penalty) Al-Ma'idah/2. Shaykh al-Islam Ibn Taymiyyah said: "And every garment that is predominantly assumed to be used to assist in disobedience: it is not permissible to sell it or sew it for someone who will use it for disobedience and oppression." And Shaykh al-Uthaymeen mentioned: "If the predominant activity of a company is unlawful: then he should not do it. And if its predominant activity is permissible: then he may do it. And if they are equal: he should not do it; giving precedence to the side of prohibition."