snapd 2.58 released to the stable channel recently (10/01/23) and with it brings the ability to prevent automatic updates, on either a per snap or all snap basis; for as long as the user desires (i.e, potentially forever).
To E.G prevent Firefox updating for a day
snap refresh --hold=24h firefox
to E.G prevent Firefox updating forever (Please update it manually at least).
snap refresh --hold firefox
To prevent all snaps updating automatically ever (With great power…):
snap refresh --hold
If you haven’t got 2.58 yet, please consider updating your distro packages packages (for distros such as Fedora), rebuilding (e.g AUR) or snap install snapd or snap refresh snapd (for Debian derivatives).
If you run
snap refresh, any snaps that have been held explicitly will not be included for updates. If you want to update a snap thats been explicitly specified, you must specify its name, e.g snap refresh firefox.
And finally, you can reverse all of these by using snap refresh --unhold, on a per snap or all snaps basis.