K-Meleon
The user.js file is an advanced way of changing preferences. You can change most settings from the browser or K-Meleon's config files. The standard way to change advanced preferences is to type about:config into the address bar and press enter. Any preferences set in user.js will override settings on the about:config page.
There are 2 advantages to editing user.js to change settings:
You can find user.js at K-Meleon > Profiles > your.profile > user.js and can open it with any text editor. There may be no settings in the file by default.
A brief guide to syntax rules:
Changes in user.js will be added to prefs.js also. To remove a preference, edit out the line in user.js and then edit out the same line in prefs.js. Both files can be opened in any text editor. The open-source text editor Notepad++ offers syntax highlighting.