Adding to Watchlist sometimes opens two additional windows:
https://commons.wikimedia.org/wiki/File:Watchlist.jpg
[[:File:Watchlist.jpg]]
https://commons.wikimedia.org/wiki/File:Watchlist-1.jpg
[[:File:Watchlist-1.jpg]]
P.S. It happens while sending thanks as well: [[T118865]]
Thanks for reporting this.
What do the two screenshots exactly show? The first one looks like the first step, and the second one what is displayed afterwards? Are they not in the same browser window or browser tab? Which browser and browser version is this about? Does that also happen after disabling any browser add-ons / extensions?
Unfortunately closing this report as no further information has been provided.
@Antanana: Please reopen this report (by changing its status) after you have provided the information asked for and if this still happens. Thanks!
This is almost always due to "clicking before the page has fully loaded", (it takes us to this interface: https://www.mediawiki.org/w/index.php?title=Foo&action=watch ) and can be reproduced with a hard-refresh (eg. ctrl-F5) and then clicking the star/tab links too soon. It's especially troublesome if we use multiple gadgets/userscripts, which take additional time to load.
@Aklapper Is there a generalized task for this? I tried searching and asking in IRC, but couldn't find anything. Something in https://phabricator.wikimedia.org/tag/mediawiki-resourceloader/ perhaps?
I don't think so. https://phabricator.wikimedia.org/T136824 is only slightly related.
+Performance as "too soon" clearly depends on latency at least.
Too clarify, you don't mean that the two windows are opened at once, right? What happens to me is that I get the confirmation form if the AJAX POST doesn't succeed on its own (or if I open the link in new tab), but I never saw two tabs opened at once.