I have switched to Vivaldi. It works. Vivaldi also has some really nice extra features. Very happy with it.

@linkinpark187 — I notice you used the word synchronization. Does Opera require signing up for that service to save passwords at all? (Although you also suggest it doesn't work anyway)

This started happening some time ago, but I had some free time today to explore it. Opera 67, Mac OS 10.14 (Mojave). Problem is described in the topic title. Maybe it's just one manifestation of more widespread problems, as the following may suggest:

I tried running Opera from Terminal ($ /Applications/Opera.app/Contents/MacOS/Opera) and got several lines saying (among some other warnings and errors):

dyld: warning, LC_RPATH @loader_path/../../../../../../../../../.. in /Applications/Opera.app/Contents/Frameworks/Opera Framework.framework/Versions/67.0.3575.79/Helpers/Opera Helper.app/Contents/MacOS/Opera Helper being ignored in restricted program because of @loader_path

I deleted the Opera application, installed a new copy, and got the same warning lines. I closed Opera, added it again to the access list in the Mac keychain for Opera Safe Storage -- no change. Closed Opera, deleted Opera Safe Storage -- no change.

Highly irritating. In Opera's (or Opera's implementation of Chromium's) quest for better security, I'm forced to write down my passwords!

Whew, I fixed it!

In Keychain Access (the OS X utility), find and highlight the offending DigiCert Root CA certificate. Open its info, open the "Trust" area, and change "Use System Defaults" to "Always Trust".

That should take care of signing in at auth.opera.com. Do the same thing for the offending Symantec certificate to get onto Twitter.

I don't think it matters with the above steps done first, but if they don't work, go to the /var/db/crls folder and delete everything there, or at least crlcache.db and ocspcache.db. Restarting the system might be necessary, too.

Again, as I said in the opening post, Opera won't even load auth.opera.com. An SSL Error message is displayed stating that its security certificate has expired. The only detail is "A root or intermediate certificate has expired". Update: It's not at all obvious how to get more detail, but I poked around and finally got this: "This certificate has an invalid issuer": https://imgur.com/1zTewhC

As I noted in the initial post, Safari reported that the certificate expires Jan 6 2016, but that it has an invalid issuer: DigiCert SHA2 Extended Validation Server CA. Similarly, Safari reports that the Twitter certificate expires May 9 2016 but is signed by an untrusted issuer: Symantec Class 3 EV SSL CA - G3. Firefox doesn't note any issues with either.

Now:
Version: 29.0.1795.47 - Opera is up to date;
Update stream: Stable;
System: Mac OS X 10.9.5 64-bit.

Still unable to load Twitter (or auth.opera.com to log in to this forum).

I think it's fair to assume that the versions are the very latest. But for form's sake, here's mine:

Version: 28.0.1750.51 - Opera is up to date
Update stream: Stable
System: Mac OS X 10.9.5 64-bit

By the way, I had downloaded Opera Developer and just now checked it again (version 30.0.1835.5). It also does not load Twitter.

Starting a few days ago, Opera won't load Twitter, returning instead an SSL Error and no apparent way to override it. It says the "security certificate is not trusted by your device's operating system." And further, "You cannot visit twitter.com right now because the website uses HSTS."

I know that Twitter has recently implemented some new security measures, but I believe that Opera uses the OS X network and security settings, and Safari (at least in OS X 10.9) loads Twitter just fine.

What should I do?

P.S. Nor could Opera load auth.opera.com, saying its certificate has expired. So I have had to use Firefox, which did not report any problem, for this posting! (Safari reported that the certificate expires Jan 6 2016 but has an invalid issuer, and Safari allows one to continue anyway.)