Firefox 86 is out, not only with multiple picture-in-picture (now have all the Weird Al videos open simultaneously!) and total cookie protection (not to be confused with other things called TCP) but also some noticeable performance improvements and finally gets rid of Backspace backing you up, a key I have never pressed to go back a page. Or, maybe those performance improvements are due to further improvements to our LTO-PGO recipe, which uses Fedora's work to get rid of the sidecar shell script. Now with this single patch, plus their change to nsTerminator.cpp to allow optimization to be unbounded by time, you can build a fully link- and profile-guided optimized version for OpenPOWER and gcc with much less work. Firefox 86 also incorporates our low-level Power-specific fix to xpconnect.

Our .mozconfigs are mostly the same except for purging a couple iffy options. Here's Optimized:

export CC=/usr/bin/gcc
export CXX=/usr/bin/g++

mk_add_options MOZ_MAKE_FLAGS="-j24"
ac_add_options --enable-application=browser
ac_add_options --enable-optimize="-O3 -mcpu=power9"
ac_add_options --enable-release
ac_add_options --enable-linker=bfd
ac_add_options --enable-lto=full
ac_add_options MOZ_PGO=1

# uncomment if you have it
#export GN=/home/censored/bin/gn

And here's Debug:

export CC=/usr/bin/gcc
export CXX=/usr/bin/g++

mk_add_options MOZ_MAKE_FLAGS="-j24"
ac_add_options --enable-application=browser
ac_add_options --enable-optimize="-Og -mcpu=power9"
ac_add_options --enable-debug
ac_add_options --enable-linker=bfd

# uncomment if you have it
#export GN=/home/censored/bin/gn

https://www.talospace.com/2021/02/firefox-86-on-power.html