Since firefox 15x.x site login random error messages: "Access Denied You don't have permission to access"

Since Firefox 15x.x on a site login I get at random error messages: "Access Denied You don't have permission to access" This happens randomly with banking, credit card sites but also news sites or any other site. Hitting the re-fresh/reload 2 or 3 times usually solves the problem and the page loads. I tried various things from cache clearing etc. and some of the other "I don't know but I have 7 steps what to do" answers from various sites, but nothing works. The problem is persistent but random. The problem is new and started to show up after the V 150 update and seems to be persistent although random in appearance. Here's a sample copy: (domain name changed to xxxxxxx) ''Access Denied You don't have permission to access "http://cardholder.xxxxxxx.com/mobilev2/auth/callback/?" on this server. Reference #18.4860d017.1790203328.6344535d https://errors.xxxxxxxxx.com/18.4860d017.1790203328.6344535d ''