You can change image animation behaviour in the following ways:
Image animation preference
The image.animation_mode preference determines how multi-frame GIF images are animated. This preference settings affects GIFs in every kind of displayed content, including web pages, messages and RSS feeds.
You can change this preference setting using any of the usual methods for editing configuration, specifically:
In Mozilla Suite and Firefox:
- In the Location Bar type about:config and hit Enter
- Type "anim" in the Filter field (to quickly find the needed preference)
- Double-click the image.animation_mode line and edit it to one of the following:
- none — will prevent image animation
- once — will let the image animate once
- normal (default) — will allow it to play over and over
In Thunderbird, use the config editor (see about:config for more information) and filter it for animation to find the preference. Setting image.animation_mode to none seems to work well with version 60.*. Another possibility is setting dom.animations-api.element-animate.enabled to false.
You can edit your user.js file to set this preference. For instance, to prevent image animation in Thunderbird, insert the following into the user.js file in your Thunderbird profile folder:
Pausing animated images
Pressing the "Esc" key on Windows (other OS may be different) will pause animated images on the current website. Note: Starting in Firefox 20, this is no longer the case due to the fix for bug 614304 unless resolved in an upcoming patch (see comment 45). The SuperStop add-on by Gavin Sharp is an alternate solution.  
The following programs have options that can turn off animation on your system:
- Norton Internet Security
- ZoneAlarm Pro
- eTrust Firewall
This feature must be turned on or off from inside the aforementioned programs, not in Firefox, Mozilla Suite, or Thunderbird.