I'm on macOS 10.13.4 with the latest JDownloader 2 build. I'm able to get Firefox (latest build) launched for captcha solving via BrowserCaptchaSolver.browsercommandline with [ "/Applications/Firefox.app/Contents/MacOS/firefox", "-app=%s" ]. Upon launching, nothing else happens. I have the latest MyJDownloader extension installed, and I've disabled all other extensions and allowed pop-ups. Chrome acts the same way. When I removed the command line to use the default browser, Safari launches with the screen telling me that I need the MyJDownloader extension for captchas, which doesn't exist, but Firefox and Chrome don't do a thing when launched for captchas. Any help is appreciated. Thanks!

[raztoki]

remove -app= as its for chrome browser in app mode (without addressbar) and not firefox.

raztoki

Thanks for the suggestion. Removing -app= doesn't fix the problem for me. Neither of these work:
[ "/Applications/Firefox.app/Contents/MacOS/firefox" ]
[ "/Applications/Google Chrome.app/Contents/MacOS/Google Chrome" ]
Still launches the browser and does nothing else. Both have MyJDownloader extension, other extensions are disabled, and pop-ups are allowed.

[Jiaz]

The "%s" is missing!

You only start the browser but there is no placeholder for the url
[ "/Applications/Firefox.app/Contents/MacOS/firefox", "%s"]

That appears to have done it! I had only tried %s with -app=. Thanks, Jiaz!

[Jiaz]

You're welcome! Thanks for the feedback!