Firstly, to get your SMB shares working again: MountWindowsSharesPermanently - Ubuntu Wiki I believe you should mount the share under
/media/<whatever>. You may need to give Firefox removable media access - I think the solution for doing this can be found from these two links: How can Snap permissions be viewed and modified? - Ask Ubuntu and https://snapcraft.io/docs/removable-media-interface
Now for a bit of why I think the change to snap was probably a good one:
I think the thinking here is, all of the features that a regular home user would expect to work out of the box, work. No tweaks needed. You can browse, download, blog, etc. on Firefox with no tweaks. If you’re using more advanced features like SMB shares, the devs assume you know what you’re doing and can stand to have to run a few commands or tweak a file or two to get things up and running.
I know it seems like this “security” feature is ridiculous, but you would be highly alarmed if you knew just how bad one humdinger of a cyberattack can be, and how easy it is to accidentally let one slip through the cracks. For instance, maybe someone’s secretary didn’t get a Firefox update as quickly as everyone else, and it left a security hole. They click on a bad website on accident (like I have so many times), which proceeds to exploit the security hole and gain access to the secretary’s system. From there, it’s able to leak sensitive emails and files, and modify data. The hacker puts in a backdoor that adds malicious LibreOffice macros onto macro-enabled LIbreOffice documents that it finds. The sysadmin comes along with his I-can-fix-anything-with-this flash drive that includes a whopping load of important macros along with various other scripts and utilities, plugs the drive into the secretary’s system to do some maintenance, then takes the drive back to his own system and launches one of his macros… and now his system is infected and the virus has root privileges to every server in the company’s network. And it all started thanks to one Firefox hole. (OK, this is a hypothetical scenario, but from what I know of information security, it’s a very plausible one.)
Now imagine that secretary’s not-so-secure Firefox was in a snap package. The secretary clicks on the malicious site, Firefox gets hacked… and then the hacker gets to stare at the inside of a snap container with no further access to any sensitive data. Sure, maybe they can try to hork passwords and gain further access that way, but it’s not as easy as the above scenario, and depending on the secretary’s setup, it might not be enough to hack into anything at all (maybe they do all their sensitive stuff in Chromium).
It might be a tiny inconvenience for you one time per system you use, but it’s very possibly a lifesaver for many, many others.