diff --git a/README.md b/README.md
index 9b13bda..9c5ff00 100644
--- a/README.md
+++ b/README.md
@@ -19,7 +19,7 @@ A browser extension that automatically gets rid of sticky elements on websites y
 
 ### Building from source
 
-You can build the extension from source, using the provided `build.sh` script, passing the argument `chrome` (for Chrome, Opera, Vivaldi, etc.) or `firefox` (for Firefox & other Gecko-based browsers).
+You can build the extension from source, using the provided `build.php` script.
 
 ### Post-installation
 
diff --git a/build.php b/build.php
new file mode 100644
index 0000000..20b8acc
--- /dev/null
+++ b/build.php
@@ -0,0 +1,56 @@
+<?php
+
+## Syntax:
+##     php build.php { <platform> | all }
+## ('all' builds for all available platforms)
+##
+## This script will create build/ and build/<platform> if needed, then will
+## copy files from src/ and src/platform/<platform> into build/<platform>/.
+## The extension can then be loaded from build/<platform>.
+
+## No platform specified.
+if ($argc < 2) {
+	echo "Syntax is:\n";
+	echo "\tphp build.php { <platform> | all }\n";
+}
+
+## Determine path to repository root.
+$root = preg_replace('/\/[^\/]+$/', '', dirname(__FILE__));
+
+## Determine what platforms are available.
+$platforms = array_filter(scandir("{$root}/src/platform/"), function ($str) {
+	return strncmp($str, ".", 1);
+});
+
+## No platform specified, or specified platform does not exist.
+## NOTE: specifying 'all' will build for all platforms.
+if ($argc < 2 || !(in_array($argv[1], $platforms) || $argv[1] == "all")) {
+	echo "Available platforms are:\n";
+	foreach ($platforms as $platform)
+		echo "\t{$platform}\n";
+	die;
+}
+
+## Build for specified platform (or for all platforms, if 'all' is given).
+if ($argv[1] == "all") {
+	foreach ($platforms as $platform) {
+		build_for_platform($platform);
+	}
+} else {
+	build_for_platform($argv[1]);
+}
+
+function build_for_platform($platform) {
+	global $root;
+	echo "Building for: {$platform}\n";
+
+	$command = "cd {$root}; ";
+	$command .= "mkdir -p build/{$platform}; ";
+	$command .= "rm -rf build/{$platform}/*; ";
+	$command .= "cp -R src/{*.js,*.html,*.css,fonts,images} build/{$platform}/; ";
+	$command .= "cp -R src/platform/{$platform}/* build/{$platform}/";
+
+	`{$command}`;
+}
+
+?>
\ No newline at end of file
diff --git a/build.sh b/build.sh
deleted file mode 100755
index 6c91683..0000000
--- a/build.sh
+++ /dev/null
@@ -1,6 +0,0 @@
-#!/bin/sh
-
-mkdir -p build/$1
-rm -rf build/$1/*
-cp -R src/{*.js,*.html,*.css,fonts,images} build/$1/
-cp -R src/platform/$1/* build/$1/
diff --git a/util/README-UTIL.md b/util/README-UTIL.md
index eaf4776..62fc1f1 100644
--- a/util/README-UTIL.md
+++ b/util/README-UTIL.md
@@ -2,15 +2,11 @@
 
 This folder contains some convenience scripts. They’re mostly for me, but may be useful for anyone who wants to contribute to developing AlwaysKillSticky, so they’re documented here for completeness.
 
-## `build-all.php`
-
-Runs `build.sh` with all available platforms. This will create a `build/` directory (in the root directory of the repository) and subdirectories for each platform, and copy files from `src/` into those subdirectories. The extension can then be loaded from those subdirectories by the appropriate kind of browser.
-
 ## `package.php`
 
 Will create `.tar.gz` and `.zip` archives in the `release/` directory (creating it if needed) of the built extension for each platform (in `build/`). The archives will be named according to platform and version (read from `manifest.json` in each platform’s build directory).
 
-Passing the `-b` flag will run `build-all.php` first, before packaging.
+Passing the `-b` flag will run `build.php all` first, before packaging.
 
 ## `compute_FontAwesome_subset.php`
 
diff --git a/util/build-all.php b/util/build-all.php
deleted file mode 100644
index 2e9d771..0000000
--- a/util/build-all.php
+++ /dev/null
@@ -1,13 +0,0 @@
-<?php
-
-$platforms = [
-	"chrome",
-	"firefox"
-];
-$root = preg_replace('/\/[^\/]+$/', '', dirname(__FILE__));
-
-foreach ($platforms as $platform) {
-	`{$root}/build.sh {$platform}`;
-}
-
-?>
\ No newline at end of file
diff --git a/util/package.php b/util/package.php
index ac8f3d6..8794406 100644
--- a/util/package.php
+++ b/util/package.php
@@ -1,14 +1,14 @@
 <?php
 
-if ($argv[1] == "-b")
-	include_once("build-all.php");
-
-$platforms = [
-	"chrome",
-	"firefox"
-];
 $root = preg_replace('/\/[^\/]+$/', '', dirname(__FILE__));
 
+if ($argv[1] == "-b")
+	include_once("{$root}/build.php");
+	
+$platforms = array_filter(scandir("{$root}/src/platform/"), function ($str) {
+	return strncmp($str, ".", 1);
+});
+
 foreach ($platforms as $platform) {
 	$manifest = JSON_decode(file_get_contents("{$root}/build/{$platform}/manifest.json"), true);
 	$version = $manifest["version"];