Oy Microsoft, No Drive-by Install Allow
Installed .Net Framework 3.5 ,but it installed .Net Assistant Framework onto Firefox, or however it managed to get installed onto your computer. There is a disable function, but they didn't bother with the uninstall function -- hello, people these days are quite tech-savy in the 21st Century.
However, there's also this:
FFOnceClick Add-ons for Firefox Here's the
How to Uninstall Microsoft .Net framework Assistant from Firefox or
This for 32bit and 64bit.
I just deleted the registry key add-on to the my Firefox; reopened my Firefox, it's no longer there.