Ctrl/Shift-click on tabs is ignored; multi-tab selection broken in 1.21.15b on Linux

[RonnyOtieno20]

Preliminary Checks

• I have read and understood the important section above.
• I have searched existing issues and avoided creating duplicates.
• I am not filing an enhancement request.
• I have checked that this issue cannot be reproduced on Mozilla Firefox.
• I have checked that this issue can be reproduced once I removed all my Mods and Custom CSS.

What happened?

Ctrl + click and Shift + click no longer multi-select tabs in Zen Browser 1.21.15b on Linux.

When either modifier is held and another tab is clicked, nothing happens at all:

• The clicked tab does not become active.
• No multi-selection occurs.
• No visual selection state appears.
• The click appears to be ignored entirely while the modifier key is held.

A normal click without Ctrl or Shift still activates the tab as expected.

I tested the immediately previous Zen release on the same machine:

• Zen 1.21.14b / Firefox 153.0.4 — multi-tab selection works correctly
• Zen 1.21.15b / Firefox 154.0 — multi-tab selection is broken

This appears to be a regression introduced between 1.21.14b and 1.21.15b.

Troubleshooting already performed:

• Reproduced in normal mode.
• Reproduced in Troubleshoot Mode.
• Extensions, Zen Mods, and custom CSS are therefore unlikely to be the cause.
• Tested the 1.21.14b Linux AppImage on the same machine.
• Multi-tab selection works normally in 1.21.14b.

The regression window includes the Firefox 154 upstream sync, which touched several tab-related files:

7f40771405d47c90fa2b9c2dd88a230abbc9effb

There is also a subsequent commit modifying Zen's tab.js patch and tab mouse-event handling:

f8daccb4c95f0e72795b29ff56f18294600fb262

These may or may not be related, but they appear potentially relevant because the broken behavior specifically concerns modifier-click handling on tabs.

Expected behavior

• Ctrl + click should add or remove individual tabs from the current multi-selection. - Shift + click should select a contiguous range of tabs.

Actual behavior

When holding Ctrl or Shift and clicking another tab, the click is ignored. The clicked tab does not activate, and no multi-tab selection occurs.

Steps to reproduce

1. Launch Zen Browser 1.21.15b on Linux.
2. Open multiple tabs in the same workspace.
3. Hold Ctrl and click another tab.
4. Alternatively, click one tab, then hold Shift and click another tab.

Screenshots and videos

No response

Version

1.21.15b

What platform are you seeing the problem on?

Linux (AppImage)

What component is this issue related to?

Tabs

Relevant log output if applicable

[tuna4ll]

Looking into the tab event handling. One thing that stands out is that Firefox handles the multi selection on the tab mousedown path, while Zen adds its own handling around the same tab mouse events through tab-js.patch.

Could this be an upstream tab.js event-ordering change in Firefox 154 that makes Zen's existing patch intercept the modifier click before Firefox's multi-selection handler gets it?

A quick bisect between the 153 and 154 tab.js changes might narrow this down.

[ashvwinn]

Cannot reproduce on Linux 1.22t
Can you provide a video reproducing the issue? Also the logs (Ctrl+Shift+J)
Another thing to try to find if its just visual or the tab arent being selected at all is to right click the tabs after selecting multiple

[Propheticus]

Tested both 1.21.15b (AUR derived package) and 1.22t (Tarball) on Linux and I cannot reproduce either.

Screencast_20260823_152353.webm

[RonnyOtieno20]

Sorry for the late response. Here's the screen recording of the issue on 15b, together with 14b (which works) for comparison

1.21.15b — broken

zen-15b.mp4

1.21.14b — working

zen-14b.mp4

[Propheticus]

It looks like your tabs are indeed not selected at all.
Any errors visible in the journal while clicking a tab? (ctrl+shift+j)

Does this also happen in a newly created space? (or a new profile you can create and switch to/from in about:profiles)

[RonnyOtieno20]

It happens on my existing spaces. I haven't tried a new profile yet either. Let me retry with the journal logs visible and on new spaces and a new profile and report back.

[RonnyOtieno20]

I completed a more thorough round of testing before replying, and I think I’ve narrowed this down substantially.

The issue is definitely profile-specific.

• On my existing/default profile, Ctrl + click and Shift + click on tabs do nothing.
• The issue still occurs in a newly created Space within that same profile.
• On a completely separate profile, multi-tab selection works normally on the same Zen 1.21.15b build.
• Troubleshoot Mode does not fix the affected profile.
• No relevant console errors appear in the journal log when I perform the broken Ctrl + click / Shift + click action.

I also cloned the affected profile so I could test destructively without risking the original.

Results on the cloned affected profile:

• Created new Spaces: no change.
• Reduced the session from roughly 310 tabs to 192 tabs: no change.
• Reset browser.uiCustomization.state: no change.
• Replaced the entire prefs.js with a fresh one: no change.
• Renamed/reset Zen's session data (zen-sessions.jsonlz4 and its backups): no change.
• Reset xulstore.json: no change.
• Reset Firefox session state (sessionstore.jsonlz4 / sessionstore-backups): no change.

So at this point it does not appear to be:

• caused simply by having a large number of tabs,
• Space-specific,
• a normal about:config preference,
• UI customization state,
• Zen session data,
• Firefox sessionstore state,
• or xulstore.json.

The important comparison remains:

• Same machine
• Same Linux install
• Same Zen 1.21.15b build
• Affected profile: modifier-click on tabs is completely ignored
• Separate profile: multi-select works normally

That makes it look like some deeper persisted state or database inside the profile is responsible.

If there are specific profile files/databases you’d like me to reset or compare next, I’m happy to test them on the cloned profile.

[Propheticus]

The fact it doesn't happen in a new profile does point at either a modification or corruption as most likely causes.

Some things to try in the cloned profile, one by one:

• go to about:support and click "clear startup cache" - grab us a copy of the support data while you're there, please. (minus your username that might be in file paths)
• Disable sidebar related changes in Zen mods and remove the mods.
• If you use custom CSS: With Zen closed remove the userChrome.css from the 'chrome' subfolder if any exists and/or remove the entry that sets toolkit.legacyUserProfileCustomizations.stylesheets true from user.js and restart.
  That pref could already be false when you "Replaced the entire prefs.js with a fresh one" but can't be sure because you could have a user.js file.
• With Zen closed remove zen-keyboard-shortcuts.json from the profile folder

[RonnyOtieno20]

Here is the requested about:support raw data from the original affected profile while running 1.21.15b.

One important update: the issue has now stopped reproducing in this profile as well.

Ctrl + click and Shift + click are currently multi-selecting tabs normally again, including in the original profile with all of my existing settings and tabs.

I did not intentionally change anything in the original profile immediately before it started working again. It began working roughly an hour after my previous round of testing.

I have not cleared the startup cache yet, since the issue stopped reproducing before I could test that step.

about:support raw data

{
  "application": {
    "name": "Zen",
    "osVersion": "Linux 7.0.0-30-generic #30-Ubuntu SMP PREEMPT_DYNAMIC Fri Jul 31 18:22:54 UTC 2026",
    "version": "1.21.15b",
    "buildID": "20260818101929",
    "userAgent": "Mozilla/5.0 (X11; Linux x86_64; rv:154.0) Gecko/20100101 Firefox/154.0",
    "safeMode": false,
    "updateChannel": "release",
    "osTheme": "Kali-Dark / Kali",
    "numTotalWindows": 1,
    "numFissionWindows": 1,
    "numRemoteWindows": 1,
    "fissionAutoStart": true,
    "fissionDecisionStatus": "enabledByDefault",
    "remoteAutoStart": true,
    "policiesStatus": 1
  },

  "environmentVariables": {
    "MOZ_ENABLE_WAYLAND": "1",
    "GDK_SCALE": "1",
    "GDK_BACKEND": "wayland,x11",
    "DISPLAY": ":0",
    "MOZ_LEGACY_PROFILES": "1",
    "MOZ_APP_LAUNCHER": "/home/username/.local/opt/zen/Zen.AppImage.1.21.15b.rollback",
    "MOZ_ASSUME_USER_NS": "1",
    "XRE_PROFILE_PATH": "",
    "XRE_PROFILE_LOCAL_PATH": "",
    "XRE_RESTARTED_BY_PROFILE_MANAGER": ""
  },

  "modifiedPreferences": {
    "browser.contentblocking.category": "standard",
    "browser.sessionstore.upgradeBackup.latestBuildID": "20260818101929",
    "browser.startup.homepage_override.mstone": "154.0",
    "browser.startup.homepage_override.buildID": "20260818101929",
    "extensions.lastAppVersion": "1.21.15b",
    "network.dns.disablePrefetch": true,
    "network.http.speculative-parallel-limit": 0,
    "network.prefetch-next": false
  },

  "lockedPreferences": {
    "browser.tabs.dragDrop.dragToPin.enabled": false,
    "browser.tabs.dragDrop.multiselectStacking": false,
    "browser.tabs.groups.hoverPreview.enabled": false,
    "browser.tabs.splitView.enabled": false,
    "fission.autostart.session": true
  },

  "accessibility": {
    "isActive": true,
    "forceDisabled": 0,
    "instantiator": ""
  },

  "startupCache": {
    "DiskCachePath": "<non-empty string>",
    "IgnoreDiskCache": false,
    "FoundDiskCacheOnInit": false,
    "WroteToDiskCache": false
  },

  "userJS": {
    "exists": false
  },

  "graphics": {
    "desktopEnvironment": "hyprland",
    "numTotalWindows": 1,
    "numAcceleratedWindows": 1,
    "windowLayerManagerType": "WebRender",
    "windowLayerManagerRemote": true,
    "adapterDescription": "AMD Radeon Graphics (radeonsi, phoenix, ACO, DRM 3.64, 7.0.0-30-generic)",
    "driverVendor": "mesa/radeonsi",
    "driverVersion": "26.0.3.0",
    "targetFrameRate": 60,
    "windowProtocol": "wayland"
  },

  "addons": [
    {
      "name": "Apollo Client Devtools",
      "version": "4.26.0",
      "isActive": true,
      "locationName": "app-profile"
    },
    {
      "name": "Bitwarden Password Manager",
      "version": "2026.8.0",
      "isActive": true,
      "locationName": "app-profile"
    },
    {
      "name": "MarkDownload - Markdown Web Clipper",
      "version": "3.2.0",
      "isActive": true,
      "locationName": "app-profile"
    },
    {
      "name": "PrintFriendly - Print, PDF, and Screenshot Web Pages",
      "version": "6.7.10",
      "isActive": true,
      "locationName": "app-profile"
    },
    {
      "name": "uBlock Origin",
      "version": "1.73.0",
      "isActive": true,
      "locationName": "app-profile"
    },
    {
      "name": "Video Download Helper",
      "version": "10.5.35.2",
      "isActive": true,
      "locationName": "app-profile"
    },
    {
      "name": "Vimium",
      "version": "2.4.2",
      "isActive": true,
      "locationName": "app-profile"
    }
  ],

  "legacyUserStylesheets": {
    "active": false,
    "types": []
  },

  "normandy": {
    "addonStudies": [],
    "prefRollouts": [],
    "prefStudies": [],
    "nimbusExperiments": [],
    "nimbusRollouts": []
  }
}