UserAgent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Firefox/52.0

Example URL:
http://www.gtalbot.org/BrowserBugsSection/CSS3Contain/contain-style-counters-004.html

Steps to reproduce the problem:
http://www.gtalbot.org/BrowserBugsSection/CSS3Contain/contain-style-counters-004.html 

What is the expected behavior?
20 should be displayed

Reference file:

http://www.gtalbot.org/BrowserBugsSection/CSS3Contain/contain-style-counters-003-ref.html

What went wrong?
0 is displayed

Does it occur on multiple sites: No

Is it a problem with a plugin? No 

Did this work before? No 

Does this work in other browsers? No
 Firefox 63.0a1 buildID=20180730221422

Chrome version: 69.0.3486.0  Channel: dev
OS Version: 
Flash Version: irrelevant

- Relevant section of spec (3.3 Style Containment)
https://www.w3.org/TR/css-contain-1/#containment-style
states
"
1. The counter-increment and counter-set properties must be scoped to the element's sub-tree and create a new counter.
"

- Counting of span descendants withOUT the involvement of 'contain: style' works as expected in

http://www.gtalbot.org/BrowserBugsSection/CSS3Contain/counter-span-descendant-004.html

while counting the span children with 'contain: style' also works as expected in

http://www.gtalbot.org/BrowserBugsSection/CSS3Contain/contain-style-counters-003.html

so the problem must be with 'contain: style' which seems to affect counter-incrementing of descendants (but not children)

- Suggested Component: Blink>Layout and Blink>CSS

- Florian Rivoal should be added to CC list