# URL Modifier by Gerbil

> Rewrite HTTP/HTTPS request URLs using regex rules — before, replace, or after the matched pattern.

Canonical page: [https://chrome-stats.com/d/url-modifier-by-gerbil](https://chrome-stats.com/d/url-modifier-by-gerbil)

## Overview

- **ID:** `url-modifier-by-gerbil`
- **Platform:** Firefox
- **Type:** Firefox add-on
- **Status:** Available
- **Publisher:** gerbil
- **Category:** web-development,privacy-security,social-communication
- **Daily users:** 5
- **Weekly downloads:** 1
- **Version:** 1.0.4
- **Last updated:** 2026-04-16
- **First published:** 2026-04-12
- **Size:** 109 KB
- **Data as of:** 2026-09-08
- **Store listing:** [Firefox Add-ons Store](https://addons.mozilla.org/firefox/addon/url-modifier-by-gerbil/)
- **Website:** [https://github.com/gerbilbyte/URL-Modifier](https://github.com/gerbilbyte/URL-Modifier)

## Description

URL Modifier sits between Firefox and the network. Every HTTP and HTTPS request — pages, scripts, images, API calls, WebSockets — passes through your rules before it reaches the server. Each rule matches a pattern in the URL and applies your modification text, in one of three modes:
* Before : Inserts your text immediately before the matched pattern
* Replace : Replaces the matched pattern with your text (supports $1, $2 capture groups)
* After : Appends your text immediately after the matched pattern
Rules are applied top-to-bottom in order. Patterns are JavaScript regular expressions, with automatic fallback to literal string matching if the regex is invalid.

Features
* Real-time URL rewriting — intercepts all request types: main_frame, sub_frame, script, image, xmlhttprequest, websocket, media, beacon, and more
* Three-layer interception — webRequest.onBeforeRequest + webNavigation.onBeforeNavigate + tabs.onUpdated, so even cold-start Intent URLs from external apps (e.g. Signal opening a link in Firefox) are always caught
* Case-insensitive matching — patterns match regardless of URL capitalisation
* Regex or literal — full JavaScript regex with capture group references, automatic literal fallback for invalid patterns
* Enable / disable per rule — toggle individual rules without deleting them
* Live URL tester — paste any URL and instantly see the rewritten result
* Import / Export — save and load your full rule set as a JSON file
* Toolbar icon — turns colourful when active, grey when inactive
* Persistent state — rules and active state survive browser restarts
* No data collection — all processing is local; nothing is sent anywhere

## Rankings

- #44,311 — Overall
- #47 — modify

## Permissions and access

### Permissions

- `storage`
- `webRequest`
- `webRequestBlocking`
- `webNavigation`
- `tabs`

### Host permissions

- `<all_urls>`

## Safety

- **Risk impact:** High risk impact
- **Risk likelihood:** High risk likelihood

### Analysis details

- Grants access to browser tabs, which can be used to track user browsing habits and history, presenting a privacy concern.
- This extension has low user count. Unpopular extensions may not be stable or safe.

> Some risk analysis details are omitted from this free response. [Upgrade to view the full analysis](https://chrome-stats.com/pricing).

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Source: [Chrome-Stats](https://chrome-stats.com/d/url-modifier-by-gerbil)