Data Loss Prevention (DLP) Endpoint Prevent 15.1 MP2 Agent or later.
Endpoint Prevent cannot detect and block copy and paste or direct/inline input into Google docs / sheets / slides.
That it works for some browsers but not others, is not an intended or supported feature of the product.
Google has a unique way of transmitting data and Endpoint Prevent does not currently support that mechanism.
Chrome and Edge are designed such that we monitor paste activity by default.
For IE and FF, we need to explicitly turn on Paste monitoring through the Global Application Monitoring page.
If IE and FF are used in default mode, for normal Gmail like Web sites, even if Paste monitoring was not turned on, if we paste sensitive text, then it is transmitted to the Web sites at some point in time and it is detected through IE HTTPS or FF HTTPS channels.
However, for these specific Google sites (docs / sheets / slides), the pasted data is not detected through clipboard monitoring.
The data is transmitted to those sites and will not be detected.