Well now; I run Puppy myself, as a day-to-day OS.
It matters not whether you run Pup from multi-session CD (which is perfect just for online banking), as a USB 'frugal' install, or as an HDD 'frugal' install. Pup's biggest advantage is that of running entirely in RAM. As we all know, the contents of RAM are 'flushed' when you power-off. Result? Any 'nasties' which you may have accrued during your 'session' disappear, like vanishing ink..!
And because you're loading Pup into RAM from compressed, 'read-only' files, you're getting a brand-new, squeaky-clean copy of Pup every time you boot.
I'm not a FireFox fan, I'll be honest; I much prefer Chrome, and the Chromium-based browsers, like SlimJet, Iron, Vivaldi, and the like. However, I know there's supposed to be a lot more extensions for FireFox which will help with security, and that sort of thing.
Essentially, though, Pup is pretty secure by the very nature of the way it runs. There's not much else in the way of additional steps you need to take.....especially if you do like some Puppians do with the multi-session disc, and d/l a fresh copy of FireFox every time they boot.
That will depend on your available bandwidth from your ISP.....and how often you need to visit your bank!
Distros:- Multiple 'Puppies'..... and Anti-X 16.1
My Puppy BLOG ~~~ My Puppy PACKAGES
Compaq Presario SR1916UK; Athlon64 X2 3800+, 3 GB RAM, WD 500GB Caviar 'Blue', 32GB Kingspec PATA SSD, Seagate 'Expansion' 3 TB USB 3.0 external HDD, ATI Radeon Xpress 200 graphics, Dell 15.1" pNp monitor (1024 x 768), TP-Link PCI-e USB 3.0 card, Belkin PCI USB 2.0 4-port card, self-powered 7-port USB 2.0 hub
Dell Inspiron 1100; 2.6 GHz P4, 1.5 GB DDR1, 64GB KingSpec IDE SSD, Intel 'Extreme' graphics, 1 TB Seagate 'Expansion' external storage, HP HD2300 webcam.