Sorry to be the bearer of bad news on this one, but I don't think getting icecat to work with webrtc is possible without a lot of engineering.
If you disable all of icecat's privacy settings and disable librejs, and load the test.webrtc.org page, it will access the camera and attempt to start webrtc, but it will soon crash. I consistently and repeatably get this error each time the webrtc test is accessing my camera on icecast.
out of memory: 0xFFFFFFFFFFFFE610 bytes requested
[Parent 557465, Gecko_IOThread] WARNING: pipe error (56): Connection reset by peer: file /home/ruben/git/gnuzilla/output/icecat-60.7.0/ipc/chromium/src/chrome/common/ipc_channel_posix.cc, line 342
[Parent 557465, Gecko_IOThread] WARNING: pipe error (62): Connection reset by peer: file /home/ruben/git/gnuzilla/output/icecat-60.7.0/ipc/chromium/src/chrome/common/ipc_channel_posix.cc, line 342
###!!! [Parent][MessageChannel] Error: (msgtype=0x160080,name=PBrowser::Msg_Destroy) Channel error: cannot send/recv
If you're determined not to use Chrome or Firefox, and want to focus on privacy while still having everything work, I think Brave may be your best bet for right now. Of course there are dozens of niche Chrome and Firefox forks like Waterfox, Pale Moon.
Even though these forks may have slightly better privacy options in some ways, maintaining a completely browser is a major engineering undertaking and it's extremely difficult for these forks to try and stay up to date on security issues.
Meanwhile, the latest Firefox versions are quite privacy focused. I used Brave for a few years but switched back to Firefox completely a few months ago.
about:configand then enteringmedia.peerconnection.enabledand enabling it