So, I don't know about setting rules beforehand that work very well universally, but what I personally think is the better method is to just slowly build up your ruleset as you use it every day. I don't think lots of people know how to do this so here it is:
1) Upon using a website you frequent, enable one root at a time until it functions properly. (or you can do the more granular per grid block enable) 2) Click umatrix, then click at the top where it says "uMatrix $ver" which will take you to the dashboard. 3) In the dashboard click on "my rules" 4) on the right click the "commit" button.
What this does is commit your changes to the permanent ruleset and websites you frequent will start to "just work". A word of warning, if you blindly commit after browsing for a while when you may have done some temporary allows on random websites, those will be commited too. So I suggest either reviewing the commits first (always a good idea) and deselecting the ones you don't want, or having a new session for each of your frequented websites that you then commit from.
I have been planning to write up a tutorial on things like this for family and friends, maybe I'll post it to show hn.
When I visit a site that doesn't work. Usually I carefully whitelist things that I am willing to whitelist until it does work. If I can't get it working, then in most cases, I don't consider the content of that site to be valuable enough to whitelist things that seem sketchy.
In the case of this site, uMatrix just flat out blocked the entire site. it's not that the side page didn't load, or that nothing happened because of, say, missing javascript. I got a huge warning page in FireFox that uMatrix was flat out blocking it. Probably because the primary site is already blacklisted, maybe?
Yes some sites will be completely blacklisted, and you have to manually whitelist them if you trust them enough to try them. I usually just skip them if they do that though.
I've found one of the best compromises is using setting uBlock Origin to advanced user mode, globally block 3rd party frames, and enabling a few extra filters that I don't know off hand.
Most sites will still mostly work, and the few that don't usually just need a CDN to be enabled (you can do this per-site).
uMatrix is not a "set and forget" thing like uBlock is. Using uMatrix really requires that you understand the (admittedly overwhelming) UI and make decisions for yourself about what you want to allow/block. Personally, I deny nearly everything third-party and make individual exceptions on a per-site basis, which I save for sites I visit regularly.
Against my better judgement, I turned off uMatrix and loaded the page. Then had a look at uMatrix.
Wow, I think we have a winner for a site with the most scripts, most 3rd party domains, and the sheer number of XHRs.
Sorry for this being off topic.