I've re-read your question and realised that I misunderstood. A tool like Adblock might be the better option as it applies the blocks on a per domain basis, this would allow your new tabs to follow the same restrictions.
It is also easy to disable temporarily as required.
This used to be a standard option in the right-click menu until recent versions. Mozilla decided to move it to prevent accidental activation.
The steps to disable images now are as follows:
about:config in the URL bar.
- Accept the warning about invalidating your warranty.
permissions.default.image into the search box on the configuration page.
- Double click on the top option.
- Change the value from
2 to the pop up.
1 - loads images automatically (the default)
2 - disables loading images automatically
You can now restart your browser to allow the new settings to take effect.