To ensure that user cannot upload files from Firefox and Google Chrome and only use Microsoft Edge - Add Firefox and Chrome to the unallowed browser list in Endpoint DLP. To ensure that this will get applied to all the users you are going to need to onboard all the devices, without the onboarding process the devices will not get the benefits from the configurations in the Endpoint DLP in Purview. https://docs.microsoft.com/en-us/microsoft-365/compliance/endpoint-dlp-learn-about?view=o365- worldwide