You can look at the filename function to see how this works.

• https://searchfox.org/mozilla-release/source/browser/extensions/screenshots/build/shot.js#374

EDIT: see also this bug.

• 1744779 - Failing to download file due to missing filename sanitation

Note that you can save the screenshot to the clipboard.

You can modify the page title via document.title e.g. via a JavaScript bookmarklet and sanitize invalid characters. You can also set Firefox to always ask where to save the downloaded file what should allow to shorten/modify the filename.

Hi cor-el,

Thank you for your very useful insights.

The JavaScript bookmarklet is promising, but it does not always work. The title on the browser changes immediately, but the downloaded file still uses the old title.

I'll try to understand why this simple bookmarklet sometimes fails:

javascript: (() => { document.title = 'Untitled'; })();

I'll come back if I find a working solution.

If the problem is with full-page screenshots, the Save Screenshot extension lets you specify the elements to include in the file name. It has some level of sanitization for characters that are illegal in file names, but I don't know whether it addresses the characters that are giving you problems. Perhaps you could use the URL instead of the title as a workaround.

• https://addons.mozilla.org/firefox/addon/savescreenshot/
• https://github.com/M-Reimer/savescreenshot/blob/master/background.js#L207

Spectacle would be a far better option if you're in KDE.

https://apps.kde.org/spectacle/