(In reply to Shaoting Huang from comment #3)
Sorry it is me again, I'm using MacOS for the replication of this bug, but still, I'm unable to replicate this.
Here is what I did,
macOS Big Sur Version 11.5.2
enable HCM thru settings
Nightly build go to address bar and type about:preference and go to Privacy & Security and enable either Strict or Custom,
the Heads up sub section is still readable and not white on white
Is there something in the steps you did not mention or missing?
You can use a tool called
mozregression, which is something we use for Mozilla code to find regression ranges. Although in this case, we want to find the fix and we can do this with
mozregression --find-fix. See here for more documentation on this tool.
Once you find the commit that fixed this (and it's probably one of the issues that Morgan mentioned in Comment 5) , we can close this issue with a comment saying which bug it was.