I am having no luck with PPS V2 working in WebGL builds, built from 2018.3.8f. Everything works beautifully in Editor but in a browser the project runs without the PPS active and actually, it doesn’t activate in a Windows EXE either.
This Linear + PPS v1 demo from Unity 2017.x runs beautifully: https://blogs.unity3d.com/2017/07/17/linear-rendering-support-with-webgl-2-0/
So I’m looking for an equivalent tech demo in WebGL that proves that Post Processing Stack V2 is working… to assure me I am not crazy to expect it to. 
Otherwise, should I be downgrading to 2017 and using PPS V1 ??? 
Wouldn’t be surprised if V2 doesn’t work in WebGL, always seems to be an afterthought. I’m currently working on a 2018/19.x update to my own PostFX stack, not released yet but out of curiosity I just checked to see if it built on WebGL and it does/does work - so at you can probably assume that PPv2 has some line of shader code somewhere that breaks WebGL & will take Unity 6 months to update 
It’s not just WebGL though… it wouldn’t work in my Windows Standalone EXE builds either (a completely different project)!
Works 100% in Editor, turns off in builds. And no one replying here, like I’m the ONLY developer this happens to?
Its not just you.
I have a project that USED to work in webgl and then stopped. I tried to make another test example, and PostProcessing works fine, so its not an incompatibility. My guess is that there is something breaking with this Package Manager.
Wish I had better news for you, but from what I can tell, once it stops working on a project, unless you slowly piece it back together in a different project, it doesn’t seem like there is a fix