If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Firefox shows the shield icon at the left end of the location/address bar in case Content Blocking is blocking content.

• click the shield icon for more details and possibly disable the protection

You can check the Web Console about what content is blocked

• "3-bar" menu button or Tools -> Web Developer
• https://support.mozilla.org/en-US/kb/tracking-protection
• https://support.mozilla.org/en-US/kb/content-blocking

Thanks for the reply.

A built-in security issue seems like a reasonable possibility. I've launched Firefox in "Safe Mode" and it didn't help, so it can't be a plug-in.

I tried switching off my Ad-blocker, but it didn't help. I clicked the "Shield" and tried turning off blocking and granting all permissions, but it didn't help. :(

Are these real GIF images or GIFV files that are actually MP4 video files?

Some websites might be converting such a GIF image automatically and you may not have support to play these files.

• https://en.wikipedia.org/wiki/Video_alternative_to_GIF

You can open the YouTube test page to check support in Firefox for playing HTML5 media.

• https://www.youtube.com/html5

You can check the Web Console (Tools -> Web Developer) for media related messages.

• https://developer.mozilla.org/en-US/Tools/Web_Console

You can check the Network Monitor to see if content is blocked or otherwise fails to load.

• https://developer.mozilla.org/en-US/Tools/Network_Monitor

If necessary use "Ctrl+F5" or "Ctrl+Shift+R" (Mac: Command+Shift+R) to reload the page and bypass the cache to generate a fresh log.

Thanks for the reply. I appreciate the feedback.

It's hard to tell if the GIFs are true GIFs, though when I upload GIFs I created myself (frame animation), they do the same thing (show a single frame, Twitter overlays a "Play" button, and the image goes black.)

The YouTube test page says all formats are supported.

I redisplayed the GIF in Twitter and opened the web console. This caught my eye (an error followed by a Warning):

Content Security Policy: Ignoring ‘x-frame-options’ because of ‘frame-ancestors’ directive. Content Security Policy: The page’s settings blocked the loading of a resource at inline (“script-src”).

I'm not sure if this is the problem, but it seems probable. Not sure how I'd fix that though. Thx.

Can you post a link to a publicly accessible page (i.e. no authentication or signing on required)?

Here is one of my posts this is occurring on (image appears for less than a second, Twitter puts a "play" button on it, and it turns black):

https://twitter.com/MugsysRapSheet/status/1138429036252794882

I am also experiencing this exact issue, even with GIFs I personally created and uploaded. Works on Chrome, works on other sites, tried clearing cache and cookies, nothing works across multiple computers.

And I notice there has been no response on the issue for over 3 weeks. Is it resolved in some way?

I am also experiencing this exact problem. I click on a GIF, and it goes to a black screen. When doing a network check, it shows that it goes on an indefinite POST, supposedly searching for a jot file... which doesn't exist.

Something within the code is causing Firefox to interpret it as something else.

Twitter converts animated GIFs to MP4 videos. Does everyone's Firefox play MP4 videos normally? YouTube has a test page that probes the formats your Firefox can play -- for MP4, you need a checkmark and blue box for H.264 here:

https://www.youtube.com/html5

Mugsy said

Animated GIFs on web pages display fine. ONLY animated GIFs *I* post turn black and ONLY in Firefox.

That seems unfair. What if you view a tweet in a private window, logged out of Twitter, with a clean cache (private windows don't share cookies or cache with regular windows)?

jscher2000 said

Twitter converts animated GIFs to MP4 videos. Does everyone's Firefox play MP4 videos normally? YouTube has a test page that probes the formats your Firefox can play -- for MP4, you need a checkmark and blue box for H.264 here: https://www.youtube.com/html5

Thx for the reply.

I must update my information that I've only recently noticed *some* GIF's posted by other people (not just me) also turn black as soon as they become "playable" (screen-centered), suggesting only certain *types* of animated GIFs are being converted into some obscure format my Firefox does not support.

I checked the YouTube link and everything is checked. Twitter is the only place I've encountered animated GIFs that won't display.

PS: I'm wondering if size (both K & dimensions) might be an issue?