The kernel has been at 5.6.19 for awhile now due to an issue affecting certain nvme drives resulting in systems not booting. This is fixed in kernel 5.10 which is currently a release candidate, when its out as a proper release, Solus can finally update the kernel.
Firefox is already at 83 in the unstable repository which Solus usually syncs to stable every Friday / Saturday depending on where you live. However sync did not occur last week due to requiring further testing for the gnome 3.38 stack update. Sync should occur this week unless a show stopper issue is found.