perf(cache): force Firefox to send cache headers

`immutable` header is only supported by Firefox and Safari.
When the resource is stale, Firefox don't send `If-None-Match` and
`If-Not-Modified-Since` headers.
This commit force Firefox to send these headers when resources are
stale.

Signed-off-by: Benjamin Gaussorgues <benjamin.gaussorgues@nextcloud.com>

Author: Altahrim

.htaccess

@@ -49,7 +49,7 @@
   # Add cache control for static resources
   <FilesMatch "\.(css|js|mjs|svg|gif|png|jpg|webp|ico|wasm|tflite)$">
     <If "%{QUERY_STRING} =~ /(^|&)v=/">
-      Header set Cache-Control "max-age=15778463, immutable"
+      Header set Cache-Control "max-age=15778463, must-revalidate, immutable"
     </If>
     <Else>
       Header set Cache-Control "max-age=15778463"

lib/public/AppFramework/Http/Response.php

@@ -89,7 +89,7 @@ public function __construct(int $status = Http::STATUS_OK, array $headers = [])
 	public function cacheFor(int $cacheSeconds, bool $public = false, bool $immutable = false) {
 		if ($cacheSeconds > 0) {
 			$cacheStore = $public ? 'public' : 'private';
-			$this->addHeader('Cache-Control', sprintf('%s, max-age=%s, %s', $cacheStore, $cacheSeconds, ($immutable ? 'immutable' : 'must-revalidate')));
+			$this->addHeader('Cache-Control', sprintf('%s, max-age=%s, %s', $cacheStore, $cacheSeconds, ($immutable ? 'must-revalidate, immutable' : 'must-revalidate')));
 
 			// Set expires header
 			$expires = new \DateTime();