After years of web development with Firefox, these are the extensions that actually improve my workflow — not the ones that just look good in a list.
Privacy + Ad Blocking
uBlock Origin (Essential)
The only ad blocker that works exactly as advertised. Open source, maintained by Raymond Hill (gorhill), does what it says without any adware-style behavior.
Key feature for developers: Medium Mode (dynamic filtering). Right-click the extension popup → Dashboard → "I am an advanced user." This lets you block entire categories of third-party scripts — useful for checking what a site loads without your usual content block.
Install: addons.mozilla.org/firefox/addon/ublock-origin
Multi-Account Containers (Mozilla)
First-party isolation done right. Separate sessions for work Gmail, personal Gmail, different AWS accounts — all in one browser window.
For developers: use a container for each project's staging environment. No cross-cookie leakage between environments.
Install: addons.mozilla.org/firefox/addon/multi-account-containers
Session and Tab Management
Tab Manager & Session Saver
Named sessions for context switching. Save your "Code Review" tabs separately from "Documentation" and "Project X" tabs. One-click to switch between sets.
Key feature: all local, no cloud sync, MIT licensed. For developers who context-switch between multiple projects throughout the day.
Install: addons.mozilla.org/firefox/addon/tab-manager-session-saver
Developer Tools Additions
Wappalyzer
Identifies technologies used by any website. Stack fingerprinting — see which framework, CDN, analytics, etc. a site uses. Useful for competitive research and inspiration.
Install: addons.mozilla.org/firefox/addon/wappalyzer
JSON Formatter
Firefox displays raw JSON in the browser with no formatting. This extension formats it with collapsible trees, links, and color coding. Essential when working with APIs.
Search "JSON Formatter" on AMO — several good ones available.
CSS Peeper
A simplified CSS viewer for design inspection. Shows colors, fonts, and spacing of selected elements in a clean sidebar. Useful when you want quick visual inspection without opening DevTools.
Productivity
Vimium
Keyboard-driven browser navigation. f to show link hints, H/L for back/forward, j/k for scrolling, T to search open tabs, b for bookmarks. Takes a few days to build muscle memory but significantly reduces mouse usage.
Install: addons.mozilla.org/firefox/addon/vimium-ff
Dark Reader (vs NightOwl)
Dark Reader: Transforms any site to dark mode via DOM manipulation. Works everywhere. Higher CPU. Occasional visual glitches.
NightOwl: Uses CSS prefers-color-scheme only. Works on sites with built-in dark mode (GitHub, HN, Notion, etc.). Lighter, less likely to break things.
If you primarily use modern developer sites: NightOwl. If you need dark mode everywhere: Dark Reader.
OneTab (or Tab Manager alternatives)
OneTab collapses all tabs into a list. Tab Manager & Session Saver is a more capable alternative (named sessions, restore specific sessions, not just "collapse everything").
Code-Related
Stylus
Inject custom CSS into any site. Useful for fixing a site's layout that bothers you, creating a custom reading mode for specific documentation sites, or applying company style guide tweaks.
Redirector
Redirect URLs automatically. Useful for always accessing a specific environment (dev vs staging vs production) or using alternative frontends for privacy.
PrivacyBadger (EFF)
Behavioral tracking protection. Unlike uBlock which uses lists, Privacy Badger learns over time what behaves like a tracker. Complementary to uBlock, not a replacement.
What I Don't Use
Grammarly: Sends your text to external servers. Too much privacy risk for code review comments. Use the VS Code extension instead.
LastPass/other cloud password managers with unknown server-side access: Bitwarden is the exception — open source, self-hostable, well-audited.
Tab suspenders: Modern Firefox with browser.tabs.unloadOnLowMemory = true handles this natively.
Start with uBlock Origin + Multi-Account Containers — these two change your browsing fundamentally. Add Tab Manager & Session Saver if you context-switch between multiple projects. Vimium if you want to go keyboard-first. Everything else is preference.
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