Is the plugin compatible with Firefox 59.0.1 ? Please find that info out from their support.

Yes, it is compatible.

http://avid.force.com/pkb/articles/en_US/compatibility/Sibelius-Scorch-plug-in-compatiblity

Calmus said

Yes, it is compatible. http://avid.force.com/pkb/articles/en_US/compatibility/Sibelius-Scorch-plug-in-compatiblity

How can you tell ? This page was updated October 2, 2017 and Firefox Quantum 57 was released Nov 14th.

To me, "Sibelius Scorch" sounds like a name from a Harry Potter book...

But I digress. Recent releases of Firefox only support these plugins:

• Shockwave Flash (you can install from Adobe)
• Widevine (installed by Firefox)
• OpenH264 (installed by Firefox)

Other plugins are only supported in the 32-bit Extended Support Release of Firefox. See: Why do Java, Silverlight, Adobe Acrobat and other plugins no longer work?

Firefox 57-59 do not support legacy extensions, either.

Therefore, it's very unlikely that you can use Sibelius Scorch in Firefox 59.