This documentation is not complete so update if needed.

Pale Moon

1. Download Pale Moon here.
2. Install Pale Moon.
3. Download Lightspark here. Ensure that Lightspark and Pale Moon are both x64 or x86
4. Go to "C:\Program Files\Lightspark" or "C:\Program Files (x86)\Lightspark" if you are using the x86 version.
5. Right click and Copy "nplightsparkplugin.dll" and "libspark.dll"
6. Open Pale Moon and go to "about:profiles". Search for Profile Folder and press Open Folder button.
7. Create "plugins" folder
8. Paste files

Many Distributions have Lightspark in their repositories (with the notable exception of Ubuntu/Debian-based ones)

Falkon

1. Install Lightspark as normal. If on Arch, simply install the AUR package.
2. In Falkon, go to Preferences > Browsing > Web Configuration and enable "Enable Pepper plugin API (PPAPI)".

Pale Moon Install Lightspark as usual. See here (https://github.com/lightspark/lightspark/issues/775#issuecomment-870985730) if stuck.

Waterfox Archlinux: install lightspark and waterfox from the AUR

Otter Archlinux: install lightspark and otter from the AUR