What us dark-mode haters are really asking for is a simple option to click.
Also, the dark mode setting in mist browsers is one search entry away. I really don't see the problem here
For the benefit of the rest of us, explain how to turn off "dark mode" when viewing specific websites that are hardwired to use it, while running Safari on iOS, or in Firefox on desktop, without installing various extensions that may not be available to users at work, or changing the way the whole OS appears.
Edit due to rate-limiting: The Firefox theme has absolutely nothing to do with how a web page is rendered. Select the light theme and go to Hackaday, or a logged-out Mastodon page, and you will find that it looks exactly the same.
Same with the peanut gallery that always pops up with helpful advice like "Just change your OS theme." Even if that would help, which it wouldn't, I'm not going to change the global OS appearance to accommodate a few asshat web designers.
Basically all browsers default to follow the operating systems appearance settings. I don't know why you're specifically asking to not change the OS settings, why would you prefer dark mode of your OS when you want the websites to be light mode?
To answer your question, I have no clue about Safari, but in Firefox you go to the settings page and right on the start page there is Language and Appearance where you can select your theme.
> when viewing specific websites that are hardwired to use it,
Yes, that is an issue. But that is not an issue of dark mode per-se, it is an issue with software quality and design decisions themselves. Some apps might implement their own theme switcher (which they should not do, but people seem to like making their own worse implementations of browser standards), others might not implement a dark or light mode to begin with.