Disproportionate share of 499 for Firefox

Hi. We were having complaints from users that our site is slow. Upon researching the logs I’ve stumbled upon the fact that Firefox produces about 80% of the 499 edge errors. In total, 499 errors represent 1.3% of all HTTP sessions. Still, upon having a couple of direct interviews with the users, they couldn’t say for sure if our site was significantly slower for them and they certainly didn’t notice any obvious error issues, even though the 499 errors represented nearly 20% of all HTTP requests.

Anyone else noticing that? Is Firefox just more aggressive with session polling?