If you don’t tell us what shortcomings you’re finding in FF, you’ve given us absolutely ZERO information on which to base a considered response.
I have no problems with FF when set up right. Adjust the security settings and add NoScript and Ghostery addons. And it will be as secure as you can get anywhere else.
The main thing is shut off the FireFox “Data collection and use” connection.
For top security I use TOR or an encrypted “Tails” stick which comes with TOR.
NoScript is the bomb that overrides everything no holds barred. But most are just too lazy to deal with it.