Can you give a public example URL? Most files i find are zipped, and unzipping and testing locally might not be the best test.

Several pages i found with various behavior but probably not set up in a manner to closely reproduce your reported behaviour:

https://github.com/stepcode/stepcode/blob/master/data/ap214e3/as1-oc-214.stp right-clicking Raw allows me to save as a step file clicking through of course displays the text again, but right-clicking anywhere on the page allows me to save the page as .stp again.

https://raw.githubusercontent.com/jbrownlee/Datasets/master/iris.csv I can right-click this link and download the file. In your case, it does not download but only displays? If so, does right-clicking the displayed file allow you to download?

If you start Firefox in Safe Mode, does that change the behaviour? Menu → Help → Restart with add-ons disabled (this does a bit more than temporarily disable add-ons, so if you have none, it may still be diagnostic)

Really appreciate your help. Here are some more specifics that might help.

Starting in SAFE mode does resolve the issue. Problematic links will then download as a file and not just text displayed in the browser. Exiting safe mode reverts to the problematic downloads.

In normal mode:

Links that point directly to a file, download the file correctly. An example is the 3224W.stp file on https://www.digikey.com/products/en?keywords=3224W-1-102ECT-ND.

Links that indirectly point to a file do not work correctly. An example is getting the STEP model file from www.keyelco.com for part number 575-4. This requires entering an e-mail address to get a download code and then the download link is available after the code is entered. Clicking the provided link results in the text file browser display. Other similar examples exist but they all require some back and forth instead of the simple file reference link.

Hope that this additional info is useful.

Aren't all goats cranky?

If starting in Safe Mode eliminates the issue, I would say there is either an extension a setting that is causing the issue. What settings FF resets in Safe Mode is undefined, except turning off hardware acceleration.

But you can turn off all extensions you have, and see if the problem goes away. Turn them on one at a time until the problem re-occurs, then check settings for that extension, or see if you can update it, replace it, or live without it. Script and ad blockers are likely to cause such an issue, so allowing a necessary script or domain, or turning off the blocker for that site may help.

https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems https://support.mozilla.org/en-US/kb/reset-preferences-fix-problems

If it isn't any extension, or you have none, creating a new user profile for Firefox may solve the problem. Then you can copy in your bookmarks, logins, and anything else strictly necessary.

If you have a user.js, userChrome.css, or userContent.css, they may contain entries which no longer function properly. You would likely know if you had these files as you would have to make them yourself.

Or you can opt to "Refresh Firefox", which wipes so much stuff you may want to back up your profile folder, just in case. https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

I personally believe all goats are cranky, but we aren't on speaking terms anymore. ;) The kids are crazy for sure.