JMM’s

about:config Notes and Settings

for Firefox

browser.tabs.closeWindowWithLastTab
I set this to “false” so closing a tab doesn’t force the browser window to close.
browser.urlbar.filter.javascript
I’ve set this to “false”, but I’m not sure if it still does anything. It’s supposed to allow you to type “javascript:” URLs, which are normally disabled for security reasons (i.e. naïve users being tricked into entering it).
browser.urlbar.showSearchSuggestionsFirst
I’ve set this to “false”.
browser.urlbar.suggest.calculator
true
browser.urlbar.suggest.quicksuggest.sponsored
false
browser.urlbar.suggest.searches
false
browser.urlbar.suggest.topsites
false
devtools.editor.keymap
emacs
extensions.pocket.enabled
false
identity.fxaccounts.enabled
Set to “false” to disable Firefox sync/accounts. Might be useful if you want to prevent accidentally sending your browsing history, passwords, and other data elsewhere.
layout.css.grid-template-masonry-value.enabled
true”. Just to test out this CSS grid value.
browser.eme.ui.enabled
media.eme.enabled
false”. Disable DRM. See https://support.mozilla.org/en-US/questions/1388341.
I’ve also set “media.gmp-widevinecdm.enabled = false” and “media.gmp-widevinecdm.visible = false”.
toolkit.legacyUserProfileCustomizations.stylesheets
true
Allows you to style your Firefox chrome layout with CSS.
ui.prefersReducedMotion
Set it to “1” to set your CSS “prefers-reduced-motion”. Can also set it to “0”.
browser.startup.homepage
about:blank
browser.privatebrowsing.promoEnabled
Set to “false”. I think this blocked a promo for Mozilla VPN (which, guess what, I already use).
browser.newtabpage.activity-stream.showSponsoredTopSites
false
browser.compactmode.show
Set to “true”. I forget why.
dom.no_unknown_protocol_error.enabled
Set to “false” to show an error when Firefox doesn’t know what to do with a URI scheme. Like this magnet link for GPL-v3
This unknown protocol page isn’t enabled by default anymore unless you switch this config. Screenshot taken on .
browser.urlbar.suggest.addons
Set to “false” to remove extension addons like the one below.
Suggestions for extensions in the URL bar. Screenshot taken 2023-12-12.
Same as above, but with suggestion removed.
image.jxl.enabled
In recent versions (possibly only Firefox Nightly) this enables JPEG-XL support. I have not yet (as of 2024-02-05) tried it.
network.disable-localhost-when-offline
File > Work Offline isn’t actually offline unless you set this to true.

Saving preferences

prefs.js inside the user profile suggests adding preferences to user.js (e.g. ~/.mozilla/firefox/xxxxxxxx.xxxxxxx/user.js). Haven’t tried it yet.