Further to the above.
Clean install of your SE 6.7.3_FCC would not work, FF6 opened and then immediately shutdown.
So removed the application, rebooted, and installed SE 6.7.1_FCC which was previously working perfectly. Now when I start it up I get the same results as 6.7.3 ... FF6 Flashes up and then closes. So once again removed it. Rebooted it.
Installed SE6.7.0_FCC, and everything works as it should do with FF6 starting up.
So from there installed 6.7.1_FCC, and again worked as should do. (Installed on top of 6.7.0_FCC)
Next step, to try 6.7.3_FCC as an upgrade as opposed to clean install. Install went as it should do and FF6 works, data sync works.
Just odd that I could not do a clean install. Going to try my Huawei M5 8.4" and see what that does.
Update on Huawei M5 8.4"
Removed existing version and did a clean install of SE_6.7.3_FCC and no issues at all. As the M5 is my main device I will stick with it, cannot be bothered to do a factory reset on the P30 Pro.