Hi vswhk, I assume you have the same mysterious error for all extensions, not just ad blockers? It would be suspicious if only certain kinds of extensions were uninstallable.

Could you test again, and watch for (hopefully) more specific error messages in Firefox's Browser Console? Here's how:

First, open the page on the Add-ons site for the extension you want to install.

Next, open the separate Browser Console window using either:

• "3-bar" menu button > Web Developer > Browser Console
• (menu bar) Tools > Web Developer > Browser Console
• (Mac) Command+Shift+j

Click the trash can icon at the upper left to clear the current messages in the window, then switch back over to the extension's page and click the Install button. Follow the process as far as Firefox will let you.

Then switch back over to the console window. Did Firefox log any errors related to the installation that you could paste into a reply here?

More info on the Browser Console: https://developer.mozilla.org/docs/Tools/Browser_Console

Content Security Policy: Directive ‘child-src’ has been deprecated. Please use directive ‘worker-src’ to control workers, or directive ‘frame-src’ to control frames respectively. [GA: ON] sendEvent {"hitType":"event","eventCategory":"AMO Addon Installs Started","eventAction":"addon","eventLabel":"AdBlocker"} amo-66fe51dca6622154488c.js:1:1253078 [install] Adding listener for onDownloadStarted amo-66fe51dca6622154488c.js:1:1253078 [install] Adding listener for onDownloadProgress amo-66fe51dca6622154488c.js:1:1253078 [install] Adding listener for onDownloadEnded amo-66fe51dca6622154488c.js:1:1253078 [install] Adding listener for onDownloadCancelled amo-66fe51dca6622154488c.js:1:1253078 [install] Adding listener for onDownloadFailed amo-66fe51dca6622154488c.js:1:1253078 [install] Adding listener for onInstallStarted amo-66fe51dca6622154488c.js:1:1253078 [install] Adding listener for onInstallProgress amo-66fe51dca6622154488c.js:1:1253078 [install] Adding listener for onInstallEnded amo-66fe51dca6622154488c.js:1:1253078 [install] Adding listener for onInstallCancelled amo-66fe51dca6622154488c.js:1:1253078 [install] Adding listener for onInstallFailed amo-66fe51dca6622154488c.js:1:1253078 Events to handle the installation initialized. amo-66fe51dca6622154488c.js:1:1253078 Event received Object { type: "onInstalling", id: "{c8476e06-0a50-41ec-a840-a2db436cf38c}", needsRestart: undefined } disco-5414ce10f32dba799747.js:1:586841 Event received <unavailable> amo-66fe51dca6622154488c.js:1:1253078 1561472750750 addons.xpi ERROR Failed to create staging directory: Unix error 13 during operation makeDir on file /Users/vincent/Library/Application Support/Firefox/Profiles/9vca4tvj.default/extensions/staged (Permission denied)((unknown module)) No traceback available Log.jsm:679 1561472750751 addons.xpi WARN Failed to install /var/folders/ns/31_bfnzn65s4w3tvg_4p8zwm0000gp/T/tmp-yw4.xpi from https://addons.mozilla.org/firefox/downloads/file/1737671/adblocker_pro-3.9.0-an+fx.xpi?src=dp-btn-primary to /Users/vincent/Library/Application Support/Firefox/Profiles/9vca4tvj.default/extensions/staged: Unix error 13 during operation makeDir on file /Users/vincent/Library/Application Support/Firefox/Profiles/9vca4tvj.default/extensions/staged (Permission denied)((unknown module)) No traceback available Event received Object { type: "onOperationCancelled", id: "{c8476e06-0a50-41ec-a840-a2db436cf38c}", needsRestart: undefined } disco-5414ce10f32dba799747.js:1:586841 Event received <unavailable> amo-66fe51dca6622154488c.js:1:1253078 1561472750753 addons.xpi WARN Failed to set permissions 755 on /Users/vincent/Library/Application Support/Firefox/Profiles/9vca4tvj.default/extensions/staged: [Exception... "Component returned failure code: 0x80520015 (NS_ERROR_FILE_ACCESS_DENIED) [nsIFile.permissions]" nsresult: "0x80520015 (NS_ERROR_FILE_ACCESS_DENIED)" location: "JS frame :: resource://gre/modules/addons/XPIInstall.jsm :: setFilePermissions :: line 853" data: no] Stack trace: setFilePermissions()@resource://gre/modules/addons/XPIInstall.jsm:853 cleanStagingDir()@resource://gre/modules/addons/XPIInstall.jsm:2628 releaseStagingDir()@resource://gre/modules/addons/XPIInstall.jsm:2598 startInstall()@resource://gre/modules/addons/XPIInstall.jsm:1569 1561472750754 addons.xpi WARN Failed to remove staging dir: [Exception... "Component returned failure code: 0x80520015 (NS_ERROR_FILE_ACCESS_DENIED) [nsIFile.remove]" nsresult: "0x80520015 (NS_ERROR_FILE_ACCESS_DENIED)" location: "JS frame :: resource://gre/modules/addons/XPIInstall.jsm :: cleanStagingDir :: line 2629" data: no] Stack trace: cleanStagingDir()@resource://gre/modules/addons/XPIInstall.jsm:2629 releaseStagingDir()@resource://gre/modules/addons/XPIInstall.jsm:2598 startInstall()@resource://gre/modules/addons/XPIInstall.jsm:1569 Sending message that cannot be cloned. Are you trying to send an XPCOM object? addonManager.js:226:13 Unexpected error after having received onOperationCancelled event Error: "Addon not found"

   c https://addons-discovery.cdn.mozilla.net/disco-5414ce10f32dba799747.js:1

disco-5414ce10f32dba799747.js:1:586841 Install error: undefined amo-66fe51dca6622154488c.js:1:1253078 Unexpected error after having received onOperationCancelled event <unavailable> amo-66fe51dca6622154488c.js:1:1253078 Error:

Hi vswhk, thank you for the info. It's a surprising number of items, but these items related to problems with permissions writing to disk stand out to me:

1561472750750 addons.xpi ERROR Failed to create staging directory: Unix error 13 during operation makeDir on file .../extensions/staged (Permission denied)((unknown module)) No traceback available Log.jsm:679

1561472750753 addons.xpi WARN Failed to set permissions 755 on .../extensions/staged: [Exception... "Component returned failure code: 0x80520015 (NS_ERROR_FILE_ACCESS_DENIED) [nsIFile.permissions]" nsresult: "0x80520015 (NS_ERROR_FILE_ACCESS_DENIED)" location: "JS frame :: resource://gre/modules/addons/XPIInstall.jsm :: setFilePermissions :: line 853" data: no]

Unexpected error after having received onOperationCancelled event <unavailable> amo-66fe51dca6622154488c.js:1:1253078

Hopefully someone more familiar with Linux MacOS will recognize what might be causing that.