他のアプリへのリンクは、デフォルトのユーザーセッションなしでFirefoxを開きます。

私はXUBUNTUを使用しています。長年私のお気に入りのディストリビューションでした。

過去1年間で奇妙な問題が発生し始めました。別のアプリケーション（Discordなど）でリンクを開くとFirefoxが開きますが、まったく新しいユーザー/セッションが表示されます。そのFirefoxウィンドウにはブックマークがなく、一般的なアプリケーションに対して開いているセッションもありません。

リンクをコピーしてブラウザに貼り付けましたが、もう一度クリックしてFirefoxを正常に開くようにしたいと思います。

関連性があるかどうかはわかりませんが、 ~/.config/mimeapps.list ファイルは次のようになります。

[Added Associations]
text/plain=sublime-text_subl.desktop;mousepad.desktop;libreoffice_writer.desktop;
image/png=gimp.desktop;firefox.desktop;ristretto.desktop;pinta.desktop;brave_brave.desktop;firefox_firefox.desktop;gimp_gimp.desktop;
application/pdf=google-chrome.desktop;pdfarranger.desktop;net.sourceforge.gscan2pdf.desktop;userapp-Firefox-MQO3L0.desktop;brave_brave.desktop;gimp.desktop;atril.desktop;xournalpp_xournalpp.desktop;
video/mp4=org.xfce.Parole.desktop;vlc_vlc.desktop;audacity.desktop;
image/jpeg=gimp.desktop;firefox_firefox.desktop;google-chrome.desktop;ristretto.desktop;pinta.desktop;gimp_gimp.desktop;
application/vnd.openxmlformats-officedocument.wordprocessingml.document=libreoffice-writer.desktop;libreoffice_writer.desktop;
application/msword=libreoffice-writer.desktop;
video/x-msvideo=vlc_vlc.desktop;org.xfce.Parole.desktop;
application/vnd.oasis.opendocument.spreadsheet=libreoffice-calc.desktop;
application/vnd.openxmlformats-officedocument.spreadsheetml.sheet=libreoffice-calc.desktop;
text/csv=libreoffice-calc.desktop;
application/zip=org.gnome.FileRoller.desktop;xarchiver.desktop;p7zip-desktop_p7zip-desktop.desktop;exo-file-manager.desktop;engrampa.desktop;
image/gif=ristretto.desktop;firefox.desktop;
application/vnd.rar=engrampa.desktop;
application/vnd.openxmlformats-officedocument.presentationml.presentation=libreoffice_impress.desktop;engrampa.desktop;
text/html=sublime-text_subl.desktop;org.xfce.mousepad.desktop;google-chrome.desktop;exo-web-browser.desktop;mousepad.desktop;firefox_firefox.desktop;userapp-Firefox-MQO3L0.desktop;
application/illustrator=inkscape.desktop;exo-file-manager.desktop;
text/css=sublime-text_subl.desktop;
image/x-eps=gimp.desktop;atril.desktop;
image/x-xcf=gimp.desktop;gimp_gimp.desktop;
image/vnd.adobe.photoshop=ristretto.desktop;
text/x-sh=mousepad.desktop;sublime-text_subl.desktop;
image/svg+xml=sublime-text_subl.desktop;ristretto.desktop;mousepad.desktop;gimp.desktop;inkscape.desktop;firefox_firefox.desktop;gimp_gimp.desktop;
application/rtf=libreoffice-writer.desktop;
model/x.stl-binary=exo-file-manager.desktop;
application/vnd.oasis.opendocument.text=libreoffice-writer.desktop;libreoffice_writer.desktop;
image/vnd.microsoft.icon=gimp.desktop;ristretto.desktop;
text/markdown=sublime-text_subl.desktop;
application/javascript=mousepad.desktop;
image/svg+xml-compressed=inkscape.desktop;
application/epub+zip=atril.desktop;
application/octet-stream=cherrytree_cherrytree.desktop;exo-file-manager.desktop;
application/x-compressed-tar=org.gnome.FileRoller.desktop;
audio/mp4=audacity.desktop;
application/vnd.appimage=exo-file-manager.desktop;
application/json=mousepad.desktop;sublime-text_subl.desktop;
application/vnd.oasis.opendocument.presentation=libreoffice_impress.desktop;
application/x-shellscript=mousepad.desktop;
application/gzip=pencil.desktop;org.gnome.FileRoller.desktop;
video/quicktime=vlc_vlc.desktop;org.xfce.Parole.desktop;
text/vnd.trolltech.linguist=sublime-text_subl.desktop;exo-web-browser.desktop;
application/xml=exo-web-browser.desktop;
text/x-scss=sublime-text_subl.desktop;mousepad.desktop;
application/vnd.ms-excel=libreoffice-calc.desktop;
audio/mpeg=vlc_vlc.desktop;audacity.desktop;
image/webp=gimp.desktop;google-chrome.desktop;
application/vnd.openshot-qt-project=openshot-qt.desktop;
text/x-c++src=sublime-text_subl.desktop;
application/x-partial-download=exo-file-manager.desktop;
application/vnd.debian.binary-package=gnome-software-local-file.desktop;
image/bmp=ristretto.desktop;
image/tiff=ristretto.desktop;
x-scheme-handler/http=exo-web-browser.desktop
x-scheme-handler/https=exo-web-browser.desktop
x-scheme-handler/ftp=userapp-Firefox-MQO3L0.desktop;
x-scheme-handler/chrome=userapp-Firefox-MQO3L0.desktop;
application/x-extension-htm=userapp-Firefox-MQO3L0.desktop;
application/x-extension-html=userapp-Firefox-MQO3L0.desktop;
application/x-extension-shtml=userapp-Firefox-MQO3L0.desktop;
application/xhtml+xml=userapp-Firefox-MQO3L0.desktop;
application/x-extension-xhtml=userapp-Firefox-MQO3L0.desktop;
application/x-extension-xht=userapp-Firefox-MQO3L0.desktop;
audio/x-wav=vlc_vlc.desktop;
application/x-7z-compressed=cherrytree_cherrytree.desktop;
video/webm=vlc_vlc.desktop;
video/x-matroska=vlc_vlc.desktop;

[Default Applications]
x-scheme-handler/tg=telegramdesktop.desktop
x-scheme-handler/viber=viber.desktop
audio/mpeg=vlc_vlc.desktop
video/mp4=vlc_vlc.desktop
x-scheme-handler/http=userapp-Firefox-MQO3L0.desktop
x-scheme-handler/https=userapp-Firefox-MQO3L0.desktop
x-scheme-handler/ftp=userapp-Firefox-MQO3L0.desktop
x-scheme-handler/chrome=userapp-Firefox-MQO3L0.desktop
text/html=userapp-Firefox-MQO3L0.desktop
application/x-extension-htm=userapp-Firefox-MQO3L0.desktop
application/x-extension-html=userapp-Firefox-MQO3L0.desktop
application/x-extension-shtml=userapp-Firefox-MQO3L0.desktop
application/xhtml+xml=userapp-Firefox-MQO3L0.desktop
application/x-extension-xhtml=userapp-Firefox-MQO3L0.desktop
application/x-extension-xht=userapp-Firefox-MQO3L0.desktop

どんな提案にも感謝します。ありがとうございます！