Step-by-Step:
1) Turn Windows Update OFF.
2) Uninstall 21H1 or 20H1 if you have already installed it.
3) Uninstall SIB (it may seem like SIB crashes but check Uninstall Programs after restart to make sure it is no longer in list of apps).
4) Once you have made sure SIB has now been uninstalled, go ahead and turn Windows Update ON.
5) Now let Windows Update check for updates which it should now find the 21H1 update.
6) Go ahead and install that 21H1 update.
7) Once it is installed and reboots back to Desktop, then install latest SIB.
Even with Firefox 89.0.1 installed, the 21H1 update and SIB installed, you shouldn't get those crashes. I still feel that SIB should be updated instead because this might be an issue going forward with every Windows Features Update. This is exactly what I did on my Windows 10 PC and it appears to be working with no issues now.