Oooh Ahhh. Firefox is swimming in a 24GB of RAM.
Memory is cheap 
I have at least a hundred tabs and FF sits at 2 GB. My money would be on a misbehaving extension.
Okay … maybe 24 extensions. 
@Beiruty
What app are you using to display the above summary.
Pudge
Standard KDE Plasma System Monitor
with this configuration–if this is the first time its’ gobbled anywhere near 24GB–extensions would be my guess too. If it’s every day my answer would shift to hardware.
Unless it’s the famous FF settings ‘acceleration’ dealio?
PS–I could open your picture in a new tab but I couldn’t ctrl+ it to a readable state so no opinion about your task manager
2 cents
You may want to check your browser extensions. 5GB are a bit much and I suspect that some may fight each other.
Have you checked DDR5 prices recently? 
If I remember correctly, I added profiling service/tool for the FF.
I generated an AI coded bash script since the FF taskmanager does not have dump to file option to the tabulated mem/cpu stats
─(12:29:45)──> firefox_stats ──(Fri,Aug28)─┘
CATEGORY MEMORY (MB) CPU % PID
------------------------------------------------------------------
All Extensions Combined N/A N/A (Inside Main/Tabs)
------------------------------------------------------------------
Tab Process 2498.9 5.1 4934
Tab Process 1253.3 0.7 90223
Tab Process 1076.8 2.4 4904
Tab Process 1063.7 0.3 65379
Tab Process 1026.4 4.5 66163
Tab Process 1006.9 0.5 62993
Tab Process 952.8 0.3 7703
Tab Process 919.4 0.8 4871
Tab Process 809.6 0.3 315433
Tab Process 775.8 0.2 58281
Tab Process 728.9 0.1 64510
Tab Process 725.2 0.2 58143
Tab Process 683.6 0.2 63969
Tab Process 672.4 0.2 37203
Tab Process 617.8 0.1 63332
Tab Process 604.3 0.1 58005
Tab Process 568.2 0.2 65150
Tab Process 542.6 0.4 62300
Tab Process 528.3 0.1 61968
Tab Process 485.1 0.0 58285
Tab Process 441.2 0.7 386816
Tab Process 438.0 0.1 64722
Tab Process 416.7 0.0 5388
Tab Process 412.4 0.0 4647
Tab Process 389.1 0.0 64920
Tab Process 362.2 0.0 58555
Tab Process 331.2 0.0 150952
Tab Process 319.2 0.0 89852
Tab Process 272.8 0.0 277466
Tab Process 241.0 0.0 312438
Tab Process 239.2 0.0 312607
Tab Process 206.9 0.0 5150
Tab Process 168.4 0.0 62987
Tab Process 134.6 0.0 66259
Tab Process 126.1 0.0 387820
Tab Process 122.9 0.0 387663
Tab Process 116.4 0.0 387996
Tab Process 115.5 0.0 388093
Tab Process 114.6 0.0 388159
------------------------------------------------------------------
Main Browser Process 1720.7 5.4 3497
Utility (rdd) 195.2 0.0 4656
Utility (utility) 76.5 0.0 5114
Utility (socket) 67.7 0.0 3994
Utility (forkserver) 30.7 0.0 4591
Main Browser Process 4.1 0.0 388435
Main Browser Process 3.3 0.0 3600Huh?.. I try to choke my browser off in a shallow puddle of RAM. Go figure. 
Extensions are using 2GB
Yes 30 active tabs. If you constantly using all of them, then all of them will need ram.
Are you constantly switching between all open tabs?
Yes. There is a way to close tab groups and then restore them on demand
I do not know bout tab groups. But if, you really actually using all thous tabs (they need to be active (play music check messages keep state etc) there is no way around, they will eat memory. And modern web pretty heavy. Its running 24 different games simultaneously.
I usually have lots of open tabs, but I do not use them all simultaneously, so they can be loaded on demand. Otherwise yes, lots of mem needed.
I can recommend to setup zram (with lz4 compression). Or use intel optane drive exclusively for swap. In your case of usage.
I already have a 32GB Swap in addition to the 64GB DDR5 RAM. No issues at all plus 1Gbps fiber-to-home link, the I can switch tabs and access the online data, like a flash.
It is nice when my new rig is capable of being ahead of the software.