How to upgrade browsers in Linux Mint without upgrading everything?

I’m running an obsolete version of Mint xfce. I know it’s silly from a security aspect but Cinnamon is the only packaged DE in Mint now, & I prefer old fave. Plain xfce isn’t enough for me. I’m going to switch to another distro “soon” with xfce as the default DE but would like to upgrade Firefox & Chromium to the latest versions.

I can download & install the latest .deb of each, & once upon a time I’d have been more inclined than I am now. Being slower, dimmer, & less patient in my old age, I’d like an easier method. I’m thinking that adding a newer repo (Debian Sid, even?) & installing from it might be an option.

What do you think? Any other methods?