说服火狐通过https发送一个if-modified-since头文件

我怎样才能说服火狐(3.0.1,如果重要的话)在一个https请求中发送一个if-modified-since头?如果请求使用纯HTTP,并且我的服务器尽职尽责地遵守它,那么它将发送头部。但是,当我使用https从同一个服务器请求相同的资源时(即,只需将URL中的http://更改为https://),那么火狐根本不会发送一个if-modified-since头。这种行为是由ssl规范强制执行的吗?

下面是一些HTTP和HTTPS请求/响应对的示例,使用实时HTTP头Firefox扩展进行拉取,但粗体部分有一些不同:

HTTP请求/响应:

http://myserver.com:30000/scripts/site.js

GET /scripts/site.js HTTP/1.1
Host: myserver.com:30000
User-Agent: Mozilla/5.0 (...) Gecko/2008070206 Firefox/3.0.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive
If-Modified-Since: Tue, 19 Aug 2008 15:57:30 GMT
If-None-Match: "a0501d1-300a-454d22526ae80"-gzip
Cache-Control: max-age=0

HTTP/1.x 304 Not Modified
Date: Tue, 19 Aug 2008 15:59:23 GMT
Server: Apache/2.2.8 (Unix) mod_ssl/2.2.8 OpenSSL/0.9.8
Connection: Keep-Alive
Keep-Alive: timeout=5, max=99
Etag: "a0501d1-300a-454d22526ae80"-gzip

HTTPS请求/响应:

https://myserver.com:30001/scripts/site.js

GET /scripts/site.js HTTP/1.1
Host: myserver.com:30001
User-Agent: Mozilla/5.0 (...) Gecko/2008070206 Firefox/3.0.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 300
Connection: keep-alive

HTTP/1.x 200 OK
Date: Tue, 19 Aug 2008 16:00:14 GMT
Server: Apache/2.2.8 (Unix) mod_ssl/2.2.8 OpenSSL/0.9.8
Last-Modified: Tue, 19 Aug 2008 15:57:30 GMT
Etag: "a0501d1-300a-454d22526ae80"-gzip
Accept-Ranges: bytes
Content-Encoding: gzip
Content-Length: 3766
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: text/javascript

更新:设置 browser.cache.disk_cache_ssl 事实上,这是个骗局(这很奇怪,因为正如尼古拉指出的,内存缓存仍然存在)。向响应中添加“cache-control:public”头也有效。谢谢!