How to use Linux / Windows safelly while saving passwords in web browser?

[Fli]

Hello,

i really like Web browsers feature to save & autofill passwords + usernames.

How can i simply and safelly secure Linux or Windows system so i dont need to worry about passwords be stolen when someone stole the computer or get physical access?

I dislike mounting an encrypted volume/storage file each time i start computer, so looking for something simple, automatic, maybe opensource

thank you