Getting slow internet response for browsers other than Safari (MacOS Mojave) I got a strange error message that might pertain to the issue: The operation couldn’t be completed. (OSStatus error -9806.)
Recently, I did do a little bit of file deletions by name (a measure to manually uninstall an app after using the app's own uninstallation tool, since it did an incomplete job) across all user libraries. Parental Controls are also active (which I can bypass, but prefer not to disable altogether), and webfilterproxyd has been using obscene amounts of RAM ever since (up to 3.5GB; averages at 1.3GB).
Other issues that subsequently arose include internet response in web browsers other than Safari is extremely slowed, and certain functions do not respond, namely…
• Opera (and its 'VPN' proxy service; it does not offer multiple proxy options anymore; download speeds are between bytes and kilobytes for the first 5 minutes or so, previously ranging between 500KBps and 5MBps.)
• Opera GX (default browser with same errors as Opera, except that when I open a link from Apple's Mail application, it does not load the webpage but rather merely launches the application. Beforehand, it would default to opening in whichever application window was closest to the top (in the application switcher), no matter the browser or privacy mode. Now, it forcefully launches Opera GX and doesn't even process the link that prompted it to launch.)
• Discord (desktop app; usually had instantaneous response, now takes two minutes to launch and 30 seconds to load pages, even if I had just visited them less than a minute earlier.)
• Dictionary (Wikipedia search, specifically. This is where I got the error message. After the error message displays, it takes 30 seconds to load any page– it used to be instantaneous.)
• Mail (Apple's email application; runs normally, except that if there is web content on an email, it takes an extra 10 seconds to load.)
Meanwhile, Safari is running faster than ever.
When dragging a Finder window's icon to a file-upload browser, it drags the window instead (unless I click and hold for 3 seconds on the icon only, before dragging).
Lastly, I'm constantly prompted to re-authenticate my Google account. I select 'continue.' It opens System Preferences and prompts me to open in Safari to authenticate. I select 'Open in Safari' and then wait a minute. Safari never opens, and even if it's already open it doesn't launch the login prompt. Instead, I get this:

I reset my PRAM 5 times this morning. So far, I can't tell the difference.
What can be done to restore the former connectivity to these apps?
I'm an intermediate-advanced user, so I can follow advanced steps.
In the event that you threw out something you shouldn't have, first thing to do would be to boot into Recovery and overlay the OS.
The reinstall from Recovery (as opposed to a full wipe &amp; install from Internet Recovery) will ensure all essential OS components are in place without changing any user data.
btw, resetting the NVRAM will do nothing at all for this type of issue.
A quick Google tells me OSStatus error -9806 is errSSLClosedAbort which sounds like an internet security component is not working properly.