Symptoms? Is it limited to when a site has Cloudflare's more aggressive protection turned on? I haven't noticed any problems I've attributed to Cloudflare, and I use Firefox exclusively.
I have more restrictive protections on. If you use just loose settings, it completes, but advanced fingerprint protection, for example, breaks captcha completion.
This is very known issue.
I was actually wondering if the stuff that Mozilla's talking about here will be used by bad bot people to try to circumvent CF's abuse protections. As I recall from when I was working with them, CF's service relies in part on being able to identify botnet attacks by doing its own fingerprinting.