Matthew Lang

Notes on the parts of Firefox beyond basic browsing — profiles, containers, privacy settings, and customization.

Profiles

Firefox supports multiple independent profiles (separate history, extensions, logins, cache):

firefox -P                       # open the profile manager
firefox -P "Work" -no-remote     # launch a specific profile in its own process
firefox -profile /path/to/dir    # launch using a profile at an explicit path

about:profiles manages profiles from within the browser — create, rename, set a default, or open one in a new window.

Containers

Multi-Account Containers (built-in feature, or the companion extension for more control) let you keep identities separated — e.g. work vs. personal Google accounts — in colored tabs that don’t share cookies/storage with each other or with normal browsing. Useful as a lighter-weight alternative to separate profiles when you just need site-level isolation, not a fully separate browser instance.

Privacy & tracking protection

• about:preferences#privacy — Enhanced Tracking Protection has Standard/Strict/Custom levels; Strict blocks more trackers and fingerprinting but occasionally breaks a site’s login flow.
• about:config — low-level prefs not exposed in the UI. Search-then-toggle; Firefox warns before you enter this page for a reason (typos here can have unexpected effects).
• Firefox Sync (about:preferences#sync) syncs bookmarks, history, passwords, open tabs, and add-ons across devices — end-to-end encrypted.

Reader Mode & Picture-in-Picture

• Reader Mode (icon in the address bar when available) strips a page down to just the article text — also has adjustable font, spacing, and a text-to-speech option.
• Picture-in-Picture pops a <video> element out into a floating always-on-top window — works on most sites without any setup, toggled from a button that appears on hover over the video.

Firefox View

Cmd/Ctrl+Shift+E or the pinned tab at the far left — recently closed tabs, tabs open on your other synced devices, and a searchable history view in one place.

Developer tools

userChrome.css customization

Firefox’s own UI (tab bar, toolbar) can be restyled with CSS once enabled:

1. about:config → set toolkit.legacyUserProfileCustomizations.stylesheets to true.
2. In the profile folder, create chrome/userChrome.css (for the browser UI) or userContent.css (for web page rendering).
3. Restart Firefox to pick up changes; edit-and-restart to iterate.

Keyboard shortcuts worth knowing

Extensions worth having

• uBlock Origin — content/ad blocking, low resource usage.
• Tree Style Tab — vertical, hierarchical tabs for heavy multi-tab workflows.
• Multi-Account Containers — official Mozilla extension, adds container management UI beyond the built-in basics.