[markussss]

I find it incredibly useful to be able to toggle styles on and off in a simple GUI, especially for these two simple global styles:

    video { /* flip video horizontally */
        transform: scaleX(-1) !important;
    }

or

    /** scale videos that were originally 4:3, but 
        were encoded as 16:9 into proper 4:3 again */
    video {
        transform: scaleX(0.75) !important;
    }

It's not extremely useful, but every time I toggle them on, I'm very happy that I added them both.

[the_pwner224]

Out of curiosity, what do you use the first flip horizontally style for?

[markussss]

To flip videos that have been flipped, or for watching a video in the mirror. Maybe it's 1 in 100 videos, or even less, but it's so nice to be able to just toggle a button that flips the video properly.

[bastawhiz]

Not OP, but there's a lot of unscrupulous videos out there that flip video horizontally to evade content matching algorithms, and plenty of videos taken on phones or web cams that get flipped as well

[pvorb]

Most video call software will show your own webcam stream flipped horizontally to make it feel like a mirror, but others will see it correctly.