Then Firefox needs to handle that better. As an end user, I don't care about the quality of the JS of the sites I want to browse - I just want it to work, and if it works in Chrome but not Firefox then I guess I'll switch to Chrome.
The GP is likely going to be triggered by those words, because... I've seen this repeated every X months/years... "Oh... yeah, you had problems in the past, but it's so much better now"... and... it rarely is. GP will just need to try out again at their own schedule and make their own determination.
I had this standard issue with desktop/laptop linux for years... "xyx doesn't work well"... "Oh yeah, it's so much better now - no problems now". Try the new recommendation - still broken.
I had a f2f with someone at a local meetup, and we got in to "xyz is subpar/broken on linux" (some gnome thing possibly). This happened to be a linux user group, and someone challenged me with "no, you're wrong, it's fine now". So... I pulled out the laptop and fired it up and showed the irritation/bug. The response - after showing that what I was saying was a bug - was a shrug and "Oh, I don't care about that - doesn't affect me". The verbal equivalent of "WONTFIX". In person.
tldr: telling people who've been burned - often for years - that things are "better now" is generally not all the productive. Most of the time, people who have specific/legit issues will figure out if/when they're fixed or tolerable enough.