Since Mozilla has started to provide an official Debian-style repository there is no reason to use snap on Ubuntu any more. Well, except if some users don't know or don't care to switch.
[1] - https://support.mozilla.org/en-US/kb/install-firefox-linux
Also known as "90% of your users". Defaults stick, and there's nothing bad enough about snaps that i'd waste time of my day adding the debian repo, trying to switch my profiles over, etc.
That was enough for me not to look into the technical merits of the clientside implementation. The few experiences I had with snap was that programs were starting slowly (Firefox) and e.g. GPU acceleration did not work (vlc). Not sure how good the sandboxing is. But I run my Firefox sandboxed by firejail and the overhead can not be felt in daily usage.
On at least 3 occasions, I became aware of this when I would open Firefox and nothing would happen, except a message that "Firefox is already running". The only resolution was to install the deb Firefox package.
A couple months ago, I needed to do a fresh install since my system got borked during the upgrade to 24.04 LTS. As usual, the Firefox snap package was installed, so I decided to give it a try.
To its credit, it actually works this time. However, it will not save images on right click or open Zoom meeting links in the desktop client. I am fairly certain this problem would disappear if I switched back to the deb package, but it's not a big enough hassle for me to bother. I can live with some workarounds for now.
Overall, I don't mind snaps, but the Firefox snap has been far more trouble than it's worth.