If you like Firefox you can still use it with the ESR version. I'm using it on a Mac and it works fine with FF Core. Firefox is working just like it did before v. 52. This is for both MacOS and Windows.
This is from the Mozilla site:
In case you’re not yet ready for this transition to happen, the ESR (Extended Support Release) of Firefox 52 will continue to support these plugins until early 2018. Click here to download Firefox ESR.
Important: The Windows 64-bit version of Firefox 52 ESR only supports the Adobe Flash and Microsoft Silverlight plugins. If you also need support for Java or other plugins, choose the Windows (32-bit) download.
I found a browser for MAC that still works with silverlight, and allows you to browse to FFCore v5.0.02 (yeah!) I am mostly a MAC person and was sad when FireFox stopped supporting it.
I used this browser in the past when I had trouble with some Java applications running, and thought - maybe, I should try it. And it works. Just thought I'd let you know. Now what I will say is that I didn't test all the functionality, but I was able to login as the admin, see and create users and review and create workflows. So I am hoping everything else works.
And while I know, it is not an officially supported browser, I'll be using it and will let you know if I run into any issues, that would force me to look for a windows OS.