Geckofx browser Google issue

See more:

VB

I have something strange happenings in my code.
I need to login to my google account but if I set up custom useragent the google signin page did not parse in the fields user email and pass.
If I let useragent by default gecko 45 then it work.
But i dont like to google see I try to do some tasks using my program so why it doesnt accept useragent? I tried like 10 nothing work.
PLEASE do not tell me to use sellenium or other browser as my code is already 5000 lines of code and I dont have head for that to change it.
thx

What I have tried:

GeckoPreferences.User["general.useragent.override"] = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.130 Safari/537.36";//randomUser;
GeckoPreferences.User["javascript.enabled"] = true;
GeckoPreferences.User["plugin.state.flash"] = 1;