I would highly advise an upgrade, if not for anything other than the fact that anything prior to 7.5.8 has a security issue.
I myself have worked closely with Eddie in the past, not to mention that I already handle your domain name management, and offer such services (
Script Installation and Maintenance).
Edge and the latest IE both have some login issues pertaining to how they changed how a date is handled in a cookie (the fix is to not check "remember me", a coding fix is in the works for v7.6.0, which is the upcoming release that we've been working on (ultimately a rewrite/springboard for newer versions down the road)).
The issue with the Facebook link, while just at work, is likely due to security settings on an internal server, whereby when it "sees" a word, it simply blocks your access to it.