It's not allowed because sitefixes in dev tools are done for as the name says sites. file:// is not the address just the protocol similar to http:// or https://

In sitefixes we have fixes for specific sites not protocols.
What you can do if you want to have some fix for local file page is to include it in your local Dark Reader under * section.
This section is applied for all the pages opened in browser.

That's the solution I use when sometimes I had to debug some page sent to me zipped. 😉

So for me it's a big NO!

An outstsnding Idea, Ive had to workaround this local rules only stuff with the persistsnce of an 8 year old who was promissed a super nintendo with the full on duck hunt package, controllers, and mario cart, but in modern times, so it cant be plugged in to the tv without bridging into an hdmi input, when his mom's not bird dogging.

Of course this is actually worse now, with the recent changes to local network calls, its the rainbow boss of the interzones watching to make sure we dont sneak our fun, dymanic css into the file:/// view .

So, one way to do this, might be extinct now, and thats to just use a real, but generic CA cert, and just treat your local lan like a web server. And yes, I hate this idea too, and yes it does suck a great deal more on windohz.

Thats why I just took the dynamic theme I liked and slapped a static version right into windohz, in the kegacy internet options (IE 7) settings. This worked pretty well, because i had dark reader in edge too, and had to make sure edge and (brave) other chromium clients never match as far as my standard dynamic theme anyway. Otherwise, edge forgets who it is, and will cause some epic cascading style collisions. Plus, god knows we can't let edge just start handling all the local stuff, like.file:/// or it'll be that directory plus the weather, and allegations of illegal chrome-urls flags and one-drive appears misconfigured! Except, thats exsctly what i did, I just opened file:// up in edge, and paased it over to the system browsee with open-in Brave Browser, which used my native node, and dark reader could just go ahead and treat it dynamkcally.

This is the only thing that worked for me, I also had an extensive blocklist set up for that ad-block extension that needs manifest v2 to run, i forget the name, but it is a must, edge likes to think it's in charge! And it is, it's in charge of the local dark reader, and keepingn the file:/// access locked up, phoning Home:// and reminding me that I cant use IE, and every single local adress "doesnt exist".

This all replaces my old workaround btw. The system as pdf's. :)