Inform me - what is Beta update channel? And what site is this.

For clarification: I am currently on the "Beta Update Channel" for my Firefox browser (on a Windows 10 desktop). This channel receives a lot of updates and I got on this channel when I had other issues while on the regular "Release" channel. My problems were fixed with a different solution and now I would like to go back (i.e. REVERT) and be on the regular release channel of Firefox so I don't get as many updates and they are fully vetted rather than being in beta mode. However, I don't want to lose any of my current Firefox info, such as favorites, history, sync, etc.

To get back on the Release channel just install the current Firefox Release https://www.mozilla.org/firefox/all/desktop-release/win64/

Your settings like Bookmarks, history, passwords, extensions, cookies etc are not in the Firefox program folder but in a separate place. https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

Inform me - what is Beta update channel? And what site is this.

There are multiple channels of Firefox as you can see on https://www.mozilla.org/firefox/all/

Release (Fx 131.0.3) < Beta (currently at Fx 132.0b8) < Nightly (Fx 133.0a1). The Developers Edition is the same as Beta but with additional developers features. Beta channel builds can get eight or so builds in testing while the Nightly channel gets checkins and updates twice a day.

There is also the ESR (short for Extended Support Release) channels. They are currently Fx 128.0.3.1esr and the old Fx 115.16.1esr. The older Firefox 115 ESR is currently being updated with Windows 7, 8, 8.1 and macOS 10.12, 10.13, 10.14 users in mind and will be updated till at least 115.21.0esr in March 2025.