fix(firefox): update install instructions to use about:debugging for regular Firefox, xpi for Dev Edition/Nightly

Made-with: Cursor

docs/INSTALLATION.md

@@ -81,10 +81,21 @@ Each key's default value points to the manifest JSON file at `%LOCALAPPDATA%\hol
 3. Drag `~/Downloads/Holesail-Browser-1.0.0.zip` onto the extensions page  
    *(or click **Load unpacked** and select the extracted folder)*
 
-### Firefox
+### Firefox (regular)
 
-1. Open `about:addons`
-2. Click the gear icon → **Install Add-on From File**
+Firefox requires extensions to be signed by Mozilla for permanent installation. Use the temporary add-on loader:
+
+1. Open `about:debugging`
+2. Click **This Firefox**
+3. Click **Load Temporary Add-on...**
+4. Select `~/Downloads/Holesail-Browser-1.0.0.zip` (or any file inside the extracted folder)
+
+> Temporary add-ons are removed when Firefox restarts — you will need to reload it each session.
+
+### Firefox Developer Edition / Nightly (permanent)
+
+1. Open `about:config` → search for `xpinstall.signatures.required` → set it to `false`
+2. Open `about:addons` → gear icon → **Install Add-on From File**
 3. Select `~/Downloads/Holesail-Browser-1.0.0.xpi`
 
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