im no pro at linux, but by request, a collection of things i picked up about using kubuntu for a bit, may add to it over time as i learn things
all this based on kubunter 22.04

firefox tweaks:
- first of all, don't use snaps. run

snap remove firefox

(this will crash plasmashell when you open the start menu dont worry about it). snaps are often badly implemented
- if you have a highdpi mousewheel, use env variable

MOZ_USE_XINPUT2=1

to be able to use it
- (this goes for all of the os, but its noticable especially in ff) set env variable

GTK_USE_PORTAL=1

! this will make even GTK apps use the KDE file picker as opposed to the horrible gnome one
- i personally put both of these in a .sh script in

/etc/profile.d

but you can put them wherever ig or just run single programs with them
- if you like autoscrolling (middle mouse scroll), you can enable it. make sure to set about:config flag

middlemouse.paste

to false
- other about:config flags:
-

browser.compactmode.show

-> true (if you want, enables Compact view again)
-

general.smoothScroll.msdPhysics.enabled

-> true (try it, theres a bunch of params to tweak but it makes smoothscroll a LOT nicer)
-

layout.frame_rate

-> set to your screen refresh!!! else youll be capped at 60 sometimes
-

ui.systemUsesDarkTheme

-> 1 (if not 1 already)
for a lot of software, you will want build tools. run

sudo apt install build-essential dkms

if you want, disable diagnostics (run

killall systemsettings

afterward to work around a bug)
if you want, you can disable autoupdates in

software-properties-qt

you should disable automounting, it's a bit jank
set your mouse profile to Flat. pointer acceleration is idiotic
you might have noticed alt+tab has a 90ms delay before the UI shows, if you want to get rid of it:

kwriteconfig5 --file ~/.config/kwinrc --group TabBox --key DelayTime 0

then

qdbus org.kde.KWin /KWin reconfigure

then reboot
if you want to get notifications for all crashes, make

~/.config/apport/settings

and

/root/.config/apport/settings

(you will need to make the folders) with the content:

[main]
unpackaged=true

kate on its own removes trailing whitespace and adds a trailing newline. this is standard, but if you dont like it (you want the file to be saved Exactly as on screen), just disable the options under Automatic Cleanups on Save
if you get applications as AppImages, you can add them to the start menu by rightclicking it and selecting Edit Applications... you can add anything in there, it essentially manages .desktop files for you (alternatively, you can get AppImageLauncher which does it for you)
for disk management, the gnome one is better for simpler things (it cant rly do encryption or LUKS well), so get it ('s called "Disks", such a gnomie name)
flameshot is nice for screenshots, simplescreenrecorder does video
for search, you can get an Everything-like experience with FSearch, or you can use Baloo (the built in one). note about Baloo, it's pretty hefty, only use it if you have a good amount of ram and storage. WARNING: if you don't want to use file content indexing, or you don't want to index everything, you're better off disabling it entirely. if baloo is enabled, Dolphin will RELY on it for extended data columns (e.g. audio file length), and if file content indexing is off (or the folder is not indexed) they will not be filled. if you disable baloo entirely it will instead load it live

one more thing. if you're EARLY in your install, or you havent installed yet, you should REALLY consider using LVM. if you chose it at install time, good! though, you still need to think about this early: the killer LVM feature is snapshots, which allow you to make proper backups of a running system. BUT, snapshots require your lvm volume group go have some free space! you could technically add a usb stick to your VG as a second PV to make that space but... yeah that will slow things down a bit. so your best bet is to shrink your filesystem a bit (you dont need much space, snapshots essentially are "the difference between whats on the drive now and what was on there at X time". you're meant to create one, then back up from the snapshot, then destroy the snapshot again)
LVM snapshots are essentially a virtual disk frozen in time, as if you unplugged the power at that time. you create one, then back up the virtual disk (can either mount its filesystem again, or make an image, etc...), then destroy it again. it's not a perfect backup (the only perfect backup is an offline backup, taken outside of the running OS), it can have half-written files, but it's far superior to doing a backup "raw" as you won't have the "rolling shutter" effect of data changing as you're looking at it. rolling shutter will DESTROY backups of any kind of database (that includes browser data!)

install gentoo

important tip + trick: remember to bash on gnome
also install neofetch for the epick screenshot

bash as in bash not the shell bash

Pro tip if you want a full feature shell use zsh and not bash which is substantially slower. If you're a UNIX shell purist or don't care about the bash features use ksh. Another option is dash which is the default shell on Debian. Please for the love of Stallman don't use bash

I would like to add to the firefox point of the thread
The environment variable trick does work and is useful for more than firefox but a more proper way to change this for firefox specifically is by changing the following settings to 1 in about:config

File picker:

widget.use-xdg-desktop-portal.file-picker

Mime handler:

widget.use-xdg-desktop-portal.mime-handler

Settings and "look and feel" aka theming to try and use the ones setup by the system:

widget.use-xdg-desktop-portal.settings

Geolocation:

widget.use-xdg-desktop-portal.location

And lastly, opening to a file:

widget.use-xdg-desktop-portal.open-uri

The last 3 aren't needed necessarily but it's good to know.

Unrelated to that, I HIGHLY recommend and it's basically a must do thing, make sure you have

gfx.webrender.all

and

media.ffmpeg.vaapi.enabled

set to true otherwise firefox won't use hardware acceleration for videos

This is sadly not applicable to nvidia users cause nvidia drivers do NOT support vaapi. However 2 translation layers exist:

libvdpau-va-gl

Uses vdpau, works on pre-turing, only h264, unmaintained, buggy, aur package only

libva-nvidia-driver

Uses CUDA, Turing+ only, is the most compatible but it has a huge asterisk at the moment.
Not bleeding edge distros ship version 0.0.8 and this will NOT WORK if you have nvidia drivers 525+, you need version 0.0.11

If you can work around all of these I highly recommend going through the struggle to get vaapi working, not only for firefox, but cause you basically have no hardware acceleration whatsoever otherwise since basically nothing supports vdpau

to add onto webrender, in my case GPU-based firefox is actually a lot less performant for most scenarios (scrolling etc). enabling "gfx.webrender.software" will force use software rendering for it. this won't kill WebGL though! whether this is more or less performant for you depends on setup, im an nvidia user with an extremely overpowered cpu so the nvidia debuff will make the choice obvious

Quick steam GAMER tip.
Steam only uses one thread to compile vulkan shaders (for basically every single game cause everything is vulkan on linux) this can result in you starting a game and waiting on the "Processing vulkan shaders" for like even an hour on games like Overwatch 2, to eliminate this make this config in the steam install directory

~/.steam/steam/steam_dev.cfg

(on ubuntu that path maybe different, also this is for the actual package no flatpaks and whatever)
and put in

unShaderBackgroundProcessingThreads [number of threads you wish to allocate] 

and restart steam.
Actual lifesaver.

Upon further testing, you might as well not use the steam pre-cache in general, I disabled and cleared mine and everything I've played runs just fine but then again I haven't tested windows games that are known to have compilation stutter like Elden Ring so your mileage may vary