ThalysNet or other accesspoints destroy my browsing experience

Solution 1:

Disable "Ask to join new networks", when selecting Wi-fi in the Network preference pane. You might also need to explicitely forget those networks if you joined them in the past, by clicking on "Advanced..." and removing any undesired network.

Once you are connected to these networks, there is no way in changing this behavior. As every request passes through their access point, they can modify it in every way they want (and return a redirect response instead for example).

Solution 2:

Unfortunately the rewriting is done by a proxy. You could try to disable automatic CaptiveNetworkSupport probing by editing /Library/Preferences/SystemConfiguration/CaptiveNetworkSupport/Settings.plist

Solution 3:

I had a similar problem after travelling on Thalys between Belgium and Netherlands. I also use Linux and Firefox. Clicking "Restore to Default" in Prefernces did not work for me. As soon as I tried to restore my homepage, it again redirected to the Thalys portal. In addition, a couple of saved pages in my Bookmarks menu also redirected to the Thalys portal.

I solved it using "Tools --> Clear Recent History". I set "Time range to clear" to "Everything" and checked all boxes under "Details". I probably should have checked the boxes and "Cleared" one by one to see what was causing the problem, but clearing the whole lot worked for me and there is no history that I need to keep.