Stylish collects and transmits all your browsing behavior over the internet in order to analyze and sell this data. Have a look at 'Stylus' which is a fork of stylish without the invasive privacy infringements.

https://robertheaton.com/2018/07/02/stylish-browser-extension-steals-your-internet-history/

According to this:
https://www.bleepingcomputer.com/news/software/2-million-users-impacted-by-new-data-collection-policy-in-stylish-browser-add-on/
https://robertheaton.com/2018/07/02/stylish-browser-extension-steals-your-internet-history/
https://www.ghacks.net/2017/05/16/stylus-is-a-stylish-fork-without-analytics/

this plugin tracks your internet traffic. This cannot be tolerated

According to this article the Stylish browser extension violates your privacy by sending your browser history to foreign servers

https://robertheaton.com/2018/07/02/stylish-browser-extension-steals-your-internet-history/

This cannot be tolerated and breaks trust. No more Stylish for me.

Spyware!. Records every keystroke, every website visited, and sends it to their server: https://robertheaton.com/2018/07/02/stylish-browser-extension-steals-your-internet-history/

For all those complaining that Stylish stopped working on FF 61: Mozilla (again) broke up things. "-moz-document" (which never left the "experimental" status) is now blocked to work on remote URL, i.e., it's useless now. Just remove the "-moz-document" lines from the scripts and they will start working again. About the URL restrictions, now Stylish requires the addresses to be input in a specific field on the bottom of the script editing Page. Of course, incorporating "-moz-document" in the script was much easier, dozens of domains could be filtered at once. Now, they have to be entered one by one. On the plus side, Stylish still has the same flexibility regarding domain definitions, including regex rules! On the plus-plus side, it doesn't depend on Mozilla's moods anymore...

Here's the solution to FF 61.0.
https://stackoverflow.com/questions/51101566/unknown-rule-moz-document-for-stylish-in-firefox-61

Not working in Firefox 61.0

Does not work on FF 61.0 -- this is a real bummer for me!

I get also the error with "Unknown @ rule: @-moz-document"

This is the line: @-moz-document domain("wordpress.org") {
...
}

The style is local / custom style.
I am on macOS 10.12.6 Sierra

Is this connect to the release notes where it says Web Extensions are now running in its own process on macOS?

The strange thing is: the very same style loaded from userstyles.org runs perfectly fine still on FF 61.0 - strange.

Does not work with FF 61.0 any more.
All my Custom styles show the error:
Unknown @ rule: @-moz-document.

Hm, seems not to be problem with FF 61
It is also with FF 60.0.2
Till a view days ago, everything worked perfect (in 60.0.2).

Custom styles not working in FF 61.0

Hi, I have the error:

Unknown @ rule: @-moz-document.

In all of my custom styles.

Слепящие ночью страницы Файрфокса и Гугла, так и продолжат ослеплять. Зятемняет то-же что и другие псевдо-затемнители - не то что надо.

Long searched for such an add-on and found hereby !! I do not understand the negative reviews for this extension so far! I'm excited, great topics, especially the dark ones for the Google homepage, because I personally find ugly the default page of Google !! Big praise to the developer!

Awsome Thank Yoy soo Much guys

Love being able to fix the horrible things Google does in Calendar and Voice. Many thanks for this add-on!

Works good. Thanks.

I love it.

One of the few addons I would ever stick to my collection, ever since upgrading to Firefox Quantum 60+ has been reporting database errors. It is otherwise unusable and the troubleshoots I have attempted provided no solution.

Meanwhile, I'm relying on anti-strain droplets from my pharmacy to aid me in reducing visual stress.