Could you check this setting:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste anim and pause while the list is filtered

(3) The image.animation_mode preference can have these values:

• normal -- loops as long as specified by the image (this is the default, right-click > Reset to restore this value)
• none -- shows first frame only
• once -- plays the animation through once, stays on last frame

jscher2000 said

Could you check this setting: (1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk. (2) In the search box above the list, type or paste anim and pause while the list is filtered (3) The image.animation_mode preference can have these values:

• normal -- loops as long as specified by the image (this is the default, right-click > Reset to restore this value)
• none -- shows first frame only
• once -- plays the animation through once, stays on last frame

Thanks that solved my problem.

Note that some animated GIF files are actually MP4 files (.gifv) that are played with the HTML5 media player.

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

And if it is by HTML5 player make sure you fully support it as all check marks should be blue on https://www.youtube.com/html5/

If not then you may not have packages installed from your package manager in your Linux distro like FFmpeg.