This takes 1 minute to do and will give 6,8% plus usable space on screen

Firefox on second run (on first run the left sidebar is not added), bars take up 10.55% of the screenshot	Cleeeeean, bar takes up 3,75% of the screenshot

https://github.com/black7375/Firefox-UI-Fix

I recommend the Proton style.

1. Create a shell script in the Plasma autostart env folder, since PIP is experimental and off by default:

mkdir -p ~/.config/plasma-workspace/env/
echo 'export KWIN_WAYLAND_SUPPORT_XX_PIP_V1=1' > ~/.config/plasma-workspace/env/kwin-pip.sh
chmod +x ~/.config/plasma-workspace/env/kwin-pip.sh

2. Log out and back in to apply.

widget.wayland.experimental.pip.enabled is on by default in Firefox 149

copy of the original reddit thread of the fix.

1. Right click an open Picture-in-Picture window. In the context menu, select "More Actions" -> "Configure Special Window Settings...". This will populate most of the window settings for you.

2. Click "Add Property..." and select "Window title". The newly added row's text field should read "Picture-in-Picture". Change the dropdown option from "Unimportant" to "Exact Match". (All PiP windows in Firefox use this title and by making it Exact Match the rule shouldn't affect any other Firefox windows.)

3. Click "Add Property..." again and this time select "Keep above other windows". The dropdown in the newly added row should be set to "Apply Initially". Select the "Yes" radio button if it isn't already.

4. Click "OK". That's it. No more manually setting Keep Above every time you open a PiP.

5. Restart your browser

It hides the lock and shield icon to check site info

1. Open about:config

2. Search for: browser.urlbar.scotchBonnet.enableOverride

3. Change from true to false

Article with the fix

1. Open about:config

2. Search for: browser.uidensity

3. Set it to: 1

This helps me organize my bookmarks a LOT

1. Make sure you have userChrome.css support enabled:

• Go to about:config
• Search for toolkit.legacyUserProfileCustomizations.stylesheets
• Set it to true

2. The file should be in the correct location:

• Go to about:support
• Find Profile Directory and click Open Directory
• Create a folder named chrome if it doesn't exist
• Create/edit userChrome.css inside the chrome folder

3. Add the following code to the file:

#editBMPanel_folderTree {
  height: auto !important;
  min-height: 400px !important; /* Adjust this value as needed */
}

• with a cleaned UI, no horizontal taskbar and a 1080p screen 700px works great, ymmv, try and see what works best

4. Restart Firefox

Before	After