Is there really nothing that can be done about this? It happens regularly, there must be a reason

I would assume that there is somewhere a reference to that folder in the Windows Registry that makes Firefox scan this folder for possible fonts (i.e. the Solidworks application has registered its own fonts).

Hmm, I assume Firefox is using a standard Windows interface to query available fonts. Could you test whether it makes any difference to hide user-installed fonts from web content? That way, if this is some kind of fingerprinting by a site you visit, we could rule that out as an explanation. Here's the preference for that:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) In the search box in the page, type or paste layout.css.font-visibility and pause while the list is filtered

Note: before Firefox 94

(3) Double-click the layout.css.font-visibility.level preference (or click the pencil button) to display an editing field, and choose a lower value, then press Enter or click the blue check mark button to save the change.

Note: starting in Firefox 94

(3) Double-click the layout.css.font-visibility.standard preference (or click the pencil button) to display an editing field, and choose a lower value, then press Enter or click the blue check mark button to save the change.

These are the recognized values:

• 1 = only expose base system fonts
• 2 = also expose fonts from optional language packs
• 3 = also expose user-installed fonts (default)

More info on about:config: Configuration Editor for Firefox.

I would assume that there is somewhere a reference to that folder in the Windows Registry that makes Firefox scan this folder for possible fonts (i.e. the Solidworks application has registered its own fonts).

Hmm, I assume Firefox is using a standard Windows interface to query available fonts. Could you test whether it makes any difference to hide user-installed fonts from web content? That way, if this is some kind of fingerprinting by a site you visit, we could rule that out as an explanation. (...)

Thank to you both for your replies; unfortunately I saw only cor-el's reply at first so I have uninstalled those Solidworks fonts thorugh the Windows interface before trying the layout.css.font-visibility.level parameter. Now, with those fonts uninstalled from Windows, the scanning activity that appeared when launching Firefox has disappeared. Now I have hidden user installed fonts to Firefox too, but until those fonts do not reinstall automagically, I don't think I will be able to tell if it's working (but if it's the case, I will update this thread); anyway, I do think it was just a standard fonts query as you both suggested.

I admit this problem was kinda stupid, though I hadn't been able to understand it yet; I hope that uninstalling those fonts as I did will solve all my other problems with programs scanning that folder.

Again, thank you a lot for your help