I am using Palemoon a fork of FIREFOX before the nonsense. I sometimes need to open a window with a different browser and have been using the OpenWith extension version by Geoff Lankow aka darktrojan
The last to work with PM. Chrome and Explorer are found automatically by the extension but I have struggled to get the extension to do the same with Edge apparently because it a newfangled (and mangled IMHO) "Universal App" .

After much head scratching I have hit upon a technique that works for me. In the app choose the ADD option and point it to cmd.exe @ "C:\Windows\System32\cmd.exe". Then in the Add Parameter section use /c start shell:AppsFolder\Microsoft.MicrosoftEdge_8wekyb3d8 bbwe!MicrosoftEdge ( at least in my 1703 version of W10)

For Palemoon the extension is available @

I do not know if the problem is evident in 'modern' versions of FF but if it is this may work.

Further info @ https://www.itworld.com/article/2943...e-browser.html