Firefox generally handles files based on the Content-Type header sent by the server with the file, although it sometimes will override that for its own reasons. Unless the server configuration broke, it usually would not send binary files as "text/plain" or other text content types Firefox thinks can be displayed in a tab.

Apologies for a self-promotional suggestion, but:

I have an extension that might help you with the issue, at least as far as diagnosing it. After you install it and click its Zzzz button to start it listening, it will log the Content-Type sent for the various downloads so you can see what the server is telling Firefox. If it is something inappropriate, like text/plain for binary files, you may be able to resolve the issue by overriding it with the correct Content-Type or a new (synthetic) Content-Type, depending on the file extension. If the file doesn't have an extension, then the add-on probably can't help with fixing the problem.

• https://addons.mozilla.org/firefox/addon/content-type-fixer/
• Source files: https://github.com/jscher2000/Content-Type-Fixer-extension/

Thanks, but Firefox has worked for years with these files and with the "Upgrade" to v 141, now it does not.

Just trying to see if this bug can be fixed or is fixed in a version not yet available in the snap repository.

Or alternately see if the longstanding, documented, process, now removed, to add file types can be restored.

If you open the Page Info dialog in one of these tabs (Ctrl+i), what "Type" is indicated?

The type is listed as text/plain. This is being served by an Apache web server and it is unlikely to get changed there.

The point is still that with Firefox v 141, it opens unknown file types in a new tab, where before, unknown file types were saved according to the save files setting.

A secondary point is that the Ubuntu snaps are just now getting to v 141, while the Firefox web site lists 144.0.2 as the current release. Which places feedback on breaking changes at least three versions out of date, possibly more. This is probably not something that can be addressed here.

Apparently, in previous versions of Firefox, there was procedure shown on, https://support.mozilla.org/en-US/kb/change-firefox-behavior-when-open-file; which is not present in the firefox 141 snap; this claimed to allow a change in behavior based on file types(extensions) and this would allow a user to set how this is handled on a per type basis. Again, probably not something that can be addressed here.

The type is listed as text/plain. This is being served by an Apache web server and it is unlikely to get changed there.

You could bring it to their attention that they are serving files incorrectly.

The point is still that with Firefox v 141, it opens unknown file types in a new tab, where before, unknown file types were saved according to the save files setting.

text/plain is not an unknown file type.

Apparently, in previous versions of Firefox, there was procedure shown on, https://support.mozilla.org/en-US/kb/change-firefox-behavior-when-open-file; which is not present in the firefox 141 snap; this claimed to allow a change in behavior based on file types(extensions) and this would allow a user to set how this is handled on a per type basis. Again, probably not something that can be addressed here.

It should still work for most Content-Type headers (excluding the generic "application/octet-stream" type) - see sample image attached. If you need to force-save one of the problem downloads so it appears on the list, you could try right-clicking the link to the download and using Save Link As.

Thank you for your time. I am sorry we are not communicating.

Firefox interprets .gcode as text/plain. I have no way of knowing if the change in Firefox was to force text/plain or to force opening the file. In either case, the behavior changed without any visible means of changing it back.

BTW, Firefox snap v 141, does not have the option of "Always open Similar Files" for any file type. Could be why the link that previously had these instructions has been deleted from the Mozilla site?

Firefox interprets .gcode as text/plain. I have no way of knowing if the change in Firefox was to force text/plain or to force opening the file. In either case, the behavior changed without any visible means of changing it back.

According to Google's AI, G-Code files are plain text files, so it may not be an error to serve them as text/plain, but obviously it is not the most useful way to serve them.

I can see a few different possibilities here:

(1) The server previously used a different Content-Type that Firefox didn't try to display in a tab, but has stopped doing that.

(2) The server previously sent Content-Disposition: attachment to bypass displaying the file in a tab, but has stopped doing that.

(3) The server still sends Content-Disposition: attachment to bypass displaying the file in a tab, but either:

(A) Firefox is not honoring it for some reason, or (B) one of your extensions is stripping attachment disposition from those downloads, allowing Firefox to display them in a tab (there are quite a few of these, https://addons.mozilla.org/firefox/search/?q=content-disposition&type=extension)

I suppose I cannot rule out something being different between Linux and Windows.

BTW, Firefox snap v 141, does not have the option of "Always open Similar Files" for any file type. Could be why the link that previously had these instructions has been deleted from the Mozilla site?

The article is still there, and when I select Linux version 141 using the controls in the right column it still mentions the old methods:

https://support.mozilla.org/en-US/kb/change-firefox-behavior-when-open-file#firefox:linux:fx141