Updated FAQ (markdown)

FAQ.md

@@ -2,6 +2,7 @@ This page provides a collection of frequently asked questions and their answers.
 
 * [Why doesn't my bridge show new contents?](#why-doesnt-my-bridge-show-new-contents)
 * [How can I make a bridge update more frequently?](#how-can-i-make-a-bridge-update-more-frequently)
+* [Firefox doesn't show feeds anymore, what can I do?](#firefox-doesnt-show-feeds-anymore-what-can-i-do)
 
 ## Why doesn't my bridge show new contents?
 
@@ -15,4 +16,15 @@ The cache duration is bridge specific and can last anywhere between five minutes
 
 You can only do that if you are hosting the RSS-Bridge instance:
 - Enable [`custom_timeout`](Custom-Configuration#custom_timeout)
-- Alternatively, change the default timeout for your bridge by modifying the `CACHE_TIMEOUT` constant in the relevant bridge file (e.g [here](https://github.com/RSS-Bridge/rss-bridge/blob/master/index.php#L24) for Twitter).
+- Alternatively, change the default timeout for your bridge by modifying the `CACHE_TIMEOUT` constant in the relevant bridge file (e.g [here](https://github.com/RSS-Bridge/rss-bridge/blob/master/index.php#L24) for Twitter).
+
+## Firefox doesn't show feeds anymore, what can I do?
+
+As of version 64, Firefox removed support for viewing Atom and RSS feeds in the browser. This results in the browser downloading the pages instead of showing contents.
+
+Further reading:
+- https://support.mozilla.org/en-US/kb/feed-reader-replacements-firefox
+- https://bugzilla.mozilla.org/show_bug.cgi?id=1477667
+
+To restore the original behavior in Firefox 64 or higher you can use following Add-on which attempts to recreate the original behavior (with some sugar on top):
+- https://addons.mozilla.org/en-US/firefox/addon/rsspreview/