Notes:
--enable-gio was removed because:

Traceback (most recent call last):
  File "/home/build/YPKG/root/firefox/build/firefox-55.0/configure.py", line 124, in <module>
    sys.exit(main(sys.argv))
  File "/home/build/YPKG/root/firefox/build/firefox-55.0/configure.py", line 29, in main
    sandbox.run(os.path.join(os.path.dirname(__file__), 'moz.configure'))
  File "/home/build/YPKG/root/firefox/build/firefox-55.0/python/mozbuild/mozbuild/configure/__init__.py", line 422, in run
    raise InvalidOptionError('Unknown option: %s' % without_value)
mozbuild.configure.options.InvalidOptionError: Unknown option: --enable-gio
*** Fix above errors and then restart with\
               "make -f client.mk build"

I wonder if it wouldn't be time to try without (was introduced with FF 48 package... now perhaps this is fixed? :

# GCC6 produces completely broken Firefox
export CFLAGS="$CFLAGS -fno-delete-null-pointer-checks -fno-lifetime-dse -fno-schedule-insns2"
export CXXFLAGS="$CXXFLAGS -fno-delete-null-pointer-checks -fno-lifetime-dse -fno-schedule-insns2"

EDIT: I did compile and use FF 55 without those CFLAGS/CXXFLAGS and I used it during a couple of hours without encountering any problem.

OK lgtm - i dont wanna risk the CFLAG change yet until I have more time to test it, so we'll try that on the next update, cheers

Thanks for the quick update to Firefox 55, running it now and it's working great! Nice to see Solus get Firefox 55 available as an update on release day and before Ubuntu/Mint :)

And Firefox 55.0.1 is available now with the following fixes (https://www.mozilla.org/en-US/firefox/55.0.1/releasenotes/):

• Fix a regression the tab restoration process (bug 1388160)

• Fix a problem causing What's new pages not to be displayed (bug 1386224)

• Fix a rendering issue with some PKCS#11 libraries (bug 1388370)

• Disable the predictor prefetch (bug 1388160)

In D779#11432, @mate-user wrote:

And Firefox 55.0.1 is available now with the following fixes (https://www.mozilla.org/en-US/firefox/55.0.1/releasenotes/):

• Fix a regression the tab restoration process (bug 1388160)

• Fix a problem causing What's new pages not to be displayed (bug 1386224)

• Fix a rendering issue with some PKCS#11 libraries (bug 1388370)

• Disable the predictor prefetch (bug 1388160)

What you don't have it yet? ppfffff....

Now I've got Firefox 55.0.1 running after updating from Software Centre, thanks!