The original idea from Bitwise was to use the RPM installed NSPR4 and NSS and some builds were built using those RPM's. I and others found that the browser would simply vanish now and again so I went back to building using the intree NSPR4 and NSS as it was more stable.
Lars, you are using an old build and at least for me. the newer builds are more stable. Various fixes were made to build with GCC 9.2.0 and different flags, including less optimization which helped stability.
You can find the build ID by going to about:support and the GCC version and configure flags by going to about:buildconfig
Edit: about:about will list all the about: URL's