I just started having the same problem for the second time in 3 months - in Waterfox I cannot log into investorvillage.com, get the same 403 forbidden error - I can sign in on other browsers (don't have any version of Firefox installed, prefer Waterfox and Brave), but not in Waterfox. I contacted the owner of that site and their customer support to inform them that something on their servers broke the site for Waterfox again but it took a month for them to get back to me the last time this happened. BTW, I can get to your Russell Brand site just fine in Waterfox - although they may have fixed the issue for Firefox since you first posted about this.
