[Bug] Switches tabs with certain sequences of keypresses/mouse clicks

[glibg10b]

Abstract

TST sometimes switches to another tab, without me picking that tab.

Steps to reproduce

I've found two ways to reproduce this:

• Select text in any way, then press Ctrl+C or Ctrl+X.
• Switch to another window, then switch back to Firefox in any way.

With the below tab list, it switches to https://wiki.gentoo.org/wiki/Category:Pages_with_template_loops.

https://wiki.gentoo.org/wiki/User:Glibg10b/Todo

https://wiki.gentoo.org/wiki/Category:Todo

https://wiki.gentoo.org/wiki/Help:Magic_words#Page_names

https://wiki.gentoo.org/wiki/Help:Namespaces
https://wiki.gentoo.org/wiki/Help:Tables
https://wiki.gentoo.org/wiki/Help:Template_sandbox_and_test_cases
https://wiki.gentoo.org/wiki/Help:Transclusion
https://wiki.gentoo.org/wiki/Category:Misused_templates
https://wiki.gentoo.org/wiki/Category:Outdated_articles
https://wiki.gentoo.org/wiki/Category:Pages_using_deprecated_source_tags
https://wiki.gentoo.org/wiki/Category:Pages_using_deprecated_templates
https://wiki.gentoo.org/wiki/Category:Pages_using_duplicate_arguments_in_template_calls
https://wiki.gentoo.org/wiki/Category:Pages_where_template_include_size_is_exceeded
https://wiki.gentoo.org/wiki/Category:Pages_with_broken_file_links
https://wiki.gentoo.org/wiki/Category:Pages_with_ignored_display_titles
https://wiki.gentoo.org/wiki/Category:Pages_with_reference_errors
https://wiki.gentoo.org/wiki/Category:Pages_with_syntax_highlighting_errors
https://wiki.gentoo.org/wiki/Category:Pages_with_template_loops
https://wiki.gentoo.org/wiki/Category:Pages_with_too_many_expensive_parser_function_calls
https://wiki.gentoo.org/wiki/Category:Stale
https://wiki.gentoo.org/wiki/Category:Stub
https://wiki.gentoo.org/wiki/Category:Todo_articles
https://wiki.gentoo.org/wiki/Category:Uploads_without_license
https://wiki.gentoo.org/wiki/Category:User_Todo_Lists
https://wiki.gentoo.org/wiki/Category:Wikify_articles
https://wiki.gentoo.org/wiki/Category:Work_in_Progress

Environment

• Platform (OS): Linux

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While writing this issue, I discovered that this was an issue with drag and drop in Firefox. I fixed it by dragging and dropping another tab (in the default tab bar). One of the symptoms was that the blue drag-and-drop line was sometimes visible in the tab bar.