I suggest posting this problem on the Mozilla Support site. They have a team of support volunteers to troubleshoot malfunctions with your currently installed version of Firefox, while this site is focused on idea submissions for future versions of Firefox (looking ahead anywhere from 8 weeks to many months).
It would be helpful to include the text of the error page or the embedded page (framed page) with the error so the team has more context. Here's a link to the new question form (for Windows/Mac/Linux): https://mzl.la/3y1vQUQ
