[Bug] Saving a file (or exporting preferences) causes FF `149.0a1` to crash, with `"backgroundSave": true`.

[RokeJulianLockhart]

What The Problem Is

When I save a file with SingleFile, firefox-nightly-149.0a1-20260218163018.x86_64 si_signo=SIGSEGV, si_code=SI_KERNELs, albeit not so hard that abrt or CoreDumpD register it:

@.Date.20260219T013842+0000.Type.Video.Origin.webm

For investigation, observe:

1. crash-stats.mozilla.org/report/index/52a0df0f-e6b0-4b21-8238-15b310260219

2. crash-stats.mozilla.org/report/index/8326d231-3dd8-4e80-9e90-bdd580260219

How To Reproduce It

Merely save a file. I would provide its exported configuration, except that ^moz-extension:\/\/[0-9A-F]{8}-[0-9A-F]{4}-[5][0-9A-F]{3}-[89AB][0-9A-F]{3}-[0-9A-F]{12}\/src\/ui\/pages\/options.html#exportButton:~:text=Export$ /i causes crash-stats.mozilla.org/report/index/81d26b0a-fe76-4a9b-9a06-3a5d60260219, too.

My Environment

• OS

  1. #!/usr/bin/env sh
     cat /etc/os-release | jc --ini | jq 'with_entries(.value |= (if type=="string" and test("^[0-9]+$") then tonumber else . end))| {VARIANT, NAME, VERSION_ID}' | yq -P

  2. NAME: Fedora Linux
     VERSION_ID: 43
     VARIANT: KDE Plasma Desktop Edition

• Browser

  Name        : firefox-nightly
  Version     : 149.0a1
  Release     : 20260218163018
  Architecture: x86_64
  Install Date: Wed 18 Feb 2026 23:52:39 GMT
  Size        : 377338756
  Signature   : (none)
  Source RPM  : firefox-nightly-149.0a1-20260218163018.src.rpm
  Build Date  : Wed 18 Feb 2026 22:10:49 GMT
  Build Host  : 07a05bc57937
  Vendor      : Mozilla

[gildas-lormeau]

I cannot reproduce the issue but I'm on macOS. Generally speaking, when an extension triggers such low-level errors, it's a bug in the browser or the operating system. Extensions are never supposed to trigger this type of bug. I recommend that you check which update caused the problem you are experiencing. You can try an older version of SingleFile (see https://addons.mozilla.org/en-US/firefox/addon/single-file/versions), but it is unlikely to work.

However, disabling Misc. > save pages in background in the options page of SingleFile might help to circumvent this issue.

[RokeJulianLockhart]

@gildas-lormeau, I've since realised that I am able to acquire an importable duplicate of my preferences via /src/ui/pages/options-editor.html:

{
    "profiles": {
        "__Default_Settings__": {
            "removeHiddenElements": false,
            "removedElementsSelector": "",
            "removeUnusedStyles": false,
            "removeUnusedFonts": true,
            "removeFrames": false,
            "blockScripts": false,
            "blockVideos": false,
            "blockAudios": false,
            "blockFonts": false,
            "blockStylesheets": false,
            "blockImages": false,
            "acceptHeaders": {
                "document": "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8",
                "script": "*/*",
                "audio": "audio/webm,audio/ogg,audio/wav,audio/*;q=0.9,application/ogg;q=0.7,video/*;q=0.6,*/*;q=0.5",
                "video": "video/webm,video/ogg,video/*;q=0.9,application/ogg;q=0.7,audio/*;q=0.6,*/*;q=0.5",
                "font": "application/font-woff2;q=1.0,application/font-woff;q=0.9,*/*;q=0.8",
                "stylesheet": "text/css,*/*;q=0.1",
                "image": "image/avif,image/webp,image/apng,image/svg+xml,image/*,*/*;q=0.8"
            },
            "saveRawPage": false,
            "insertMetaCSP": false,
            "saveToClipboard": false,
            "addProof": true,
            "woleetKey": "",
            "saveToGDrive": false,
            "saveToDropbox": false,
            "saveWithWebDAV": false,
            "webDAVURL": "",
            "webDAVUser": "",
            "webDAVPassword": "",
            "saveWithMCP": false,
            "mcpServerUrl": "",
            "mcpAuthToken": "",
            "saveToGitHub": false,
            "githubToken": "",
            "githubUser": "",
            "githubRepository": "SingleFile-Archives",
            "githubBranch": "main",
            "saveWithCompanion": false,
            "sharePage": false,
            "compressHTML": true,
            "insertTextBody": true,
            "insertEmbeddedImage": false,
            "insertEmbeddedScreenshotImage": true,
            "compressCSS": false,
            "groupDuplicateStylesheets": false,
            "moveStylesInHead": false,
            "loadDeferredImages": true,
            "loadDeferredImagesMaxIdleTime": 1500,
            "loadDeferredImagesKeepZoomLevel": false,
            "loadDeferredImagesDispatchScrollEvent": false,
            "loadDeferredImagesBeforeFrames": false,
            "contextMenuEnabled": true,
            "filenameTemplate": "%if-empty<{page-title}|No title> ({date-locale} {time-locale}).{filename-extension}",
            "filenameMaxLength": "192",
            "filenameMaxLengthUnit": "bytes",
            "filenameReplacementCharacter": "_",
            "replaceEmojisInFilename": false,
            "saveFilenameTemplateData": true,
            "shadowEnabled": true,
            "maxResourceSizeEnabled": false,
            "maxResourceSize": 10,
            "networkTimeout": 0,
            "confirmFilename": true,
            "filenameConflictAction": "uniquify",
            "displayInfobar": true,
            "displayStats": true,
            "backgroundSave": true,
            "autoSaveDelay": 1,
            "autoSaveLoad": false,
            "autoSaveUnload": false,
            "autoSaveDiscard": false,
            "autoSaveRemove": false,
            "autoSaveLoadOrUnload": true,
            "autoSaveRepeat": false,
            "autoSaveRepeatDelay": 10,
            "autoSaveExternalSave": false,
            "removeAlternativeFonts": true,
            "removeAlternativeImages": true,
            "removeAlternativeMedias": false,
            "saveCreatedBookmarks": false,
            "passReferrerOnError": false,
            "replaceBookmarkURL": true,
            "allowedBookmarkFolders": [
                ""
            ],
            "ignoredBookmarkFolders": [
                ""
            ],
            "compressContent": true,
            "createRootDirectory": false,
            "preventAppendedData": false,
            "selfExtractingArchive": true,
            "extractDataFromPage": false,
            "password": "",
            "groupDuplicateImages": true,
            "imageReductionFactor": "1",
            "infobarTemplate": "",
            "blockMixedContent": false,
            "saveOriginalURLs": true,
            "includeInfobar": true,
            "openInfobar": false,
            "removeSavedDate": false,
            "confirmInfobarContent": false,
            "autoClose": false,
            "openEditor": false,
            "openSavedPage": true,
            "autoOpenEditor": false,
            "defaultEditorMode": "normal",
            "applySystemTheme": true,
            "contentWidth": "70",
            "warnUnsavedPage": true,
            "displayInfobarInEditor": false,
            "saveToRestFormApi": false,
            "saveToRestFormApiUrl": "",
            "saveToRestFormApiToken": "",
            "saveToRestFormApiFileFieldName": "",
            "saveToRestFormApiUrlFieldName": "",
            "saveToS3": false,
            "S3Domain": "s3.amazonaws.com",
            "S3Region": "",
            "S3Bucket": "",
            "S3AccessKey": "",
            "S3SecretKey": "",
            "customShortcut": null,
            "loadDeferredImagesBlockCookies": false,
            "loadDeferredImagesBlockStorage": false,
            "filenameReplacedCharacters": [
                "~",
                "+",
                "?",
                "%",
                "*",
                ":",
                "|",
                "\"",
                "<",
                ">",
                "\\\\",
                "\u0000-\u001f",
                "�"
            ],
            "tabMenuEnabled": true,
            "browserActionMenuEnabled": true,
            "logsEnabled": true,
            "progressBarEnabled": true,
            "maxSizeDuplicateImages": 524288,
            "forceWebAuthFlow": false,
            "resolveFragmentIdentifierURLs": false,
            "userScriptEnabled": false,
            "saveFavicon": true,
            "includeBOM": false,
            "insertMetaNoIndex": false,
            "insertSingleFileComment": true,
            "blockAlternativeImages": true,
            "delayBeforeProcessing": 0,
            "_migratedTemplateFormat": true,
            "resolveLinks": true,
            "filenameReplacementCharacters": [
                "～",
                "＋",
                "？",
                "％",
                "＊",
                "：",
                "｜",
                "＂",
                "＜",
                "＞",
                "＼"
            ],
            "delayAfterProcessing": 0,
            "infobarPositionAbsolute": false,
            "infobarPositionTop": "16px",
            "infobarPositionRight": "16px",
            "infobarPositionBottom": "",
            "infobarPositionLeft": "",
            "removeNoScriptTags": true
        }
    },
    "rules": [
        {
            "url": "file:",
            "profile": "__Default_Settings__",
            "autoSaveProfile": "__Disabled_Settings__"
        }
    ],
    "maxParallelWorkers": 12,
    "processInForeground": false
}

With that as a basis, indeed, s/"backgroundSave": true/"backgroundSave": false/g remediates it! How did you know to think of that? If you can diagnose this, I'll file a report with Mozilla.

[gildas-lormeau]

I thought about it because this isn't the first time this option has fixed problems related to downloads in general.

I have attached a zip file containing a very simple extension that is supposed to reproduce the bug. If it crashes in the same way on your machine, then I recommend attaching it to the bug report for Mozilla since it isolates the bug. The procedure for testing the extension is described here: https://extensionworkshop.com/documentation/develop/temporary-installation-in-firefox/

test-extension.zip

[RokeJulianLockhart]

@gildas-lormeau, I've filed bugzilla.mozilla.org/show_bug.cgi?id=2018809. That was of significant assistance! Should I close this (as duplicate), or should that option be disabled?

[gildas-lormeau]

I'm glad to hear that the bug can be reproduced with the test extension. We can keep the issue open until Mozilla fixes it.