Could probably merge this one as well, as like many people in this thread it is asking for one of the primary features of the FF Multi-Account Container plugin:
https://orionfeedback.org/d/4417-option-to-have-certains-urls-to-be-opened-in-defined-profile
Just these two threads (and I'm sure there's more) have over 300 votes, making this general idea the most highly voted submission by a decent margin.
@h2flux I think had the right idea in 2021 re: Profiles vs Containers, basically Profiles is the encompassing browsing session (eg "Work", "School", "Personal", etc), and then Containers are URL-defined, quaratined tabs within those sessions. For example, I have YouTube and other social media accounts for work, but I also have my personal YouTube/etc accounts. Separating these two into "Work" and "Personal" Profiles is beneficial from a tab/window organization standpoint, and Containers are strictly a tool to quarantine cookies and the like, not for organization. This lets the feature of automatic URL-defined Container not be hamstrung by multiple user accounts on the same domain, which is the case in FF Containers. In FF, if you want to have two "YouTube" tabs with separate Containers (eg a work YT account and a personal YT account), you cannot have automatic URL-based opening for both. I know many of us have this issue with Gmail as well. Orion's general browsing segregation by profiles would accomplish this by default if Containers were an aspect of individual Profiles and did not share configuration across profiles, which I assume is the existing functionality for other Profile data and config. With just this one extra layer of quarantine I think users could combine them in various ways to achieve their intended uses without needing wider featureset from devs. As far as UI/UX goes, I think many of us don't really care that much as the main function here is intended to be automatic, and Profiles has an existing UI that I think works just fine and could be mostly copied for Container config, both are mostly a one-time thing per item and not a part of everyday browsing.
tl;dr this feature is the most popular in the Suggestions list by a significant margin. I totally get the limited resources, but if we're going off Suggestion popularity, this is clearly the frontrunner.