Having the browser generate the CSR is the wrong way to do it (in my opinion) because the private key is hidden within the browser.
There is a way to generate the CSR outside of the browser which then allows you to use any browser on any OS on any computer. See Sectigo Code Signing Certificate Problems - #3 by Mike_D (Note: i did this with Sectigo. I don’t know if LeaderSSL supports this alternative method)