This seems to be pretty browser specific. Some documentation about which browser is considered would help translating the instructions.
Yes, those are IE specific. I'm guessing you're thinking about the 'Script ActiveX controls marked safe for scripting' part? We tried to find Microsoft documentation on the Windows localization for that string but without luck. If there's a suggestion for a better wording, we'd appreciate hearing about it on Github https://github.com/mathjax/MathJax-i18n/.