The extension could not be put in place

Everything before the last step worked: the file came from the store, its signature checked out and its manifest was read. What failed is moving the finished folder to where the browser reads it, and the text in brackets is what the system said.

The last step is a move

The extension is unpacked next door first and only then moved into place, so a bad download never touches the copy that already works.

This line means the unpacked folder is fine and the move is what did not go through.

A running profile holds the folder

A browser that has this extension loaded keeps its folder open, and an open folder cannot be renamed on Windows.

Close every profile that uses it and press Install again. This is the most common cause by a wide margin.

No room or no rights

A full disk and a folder the account cannot write to fail at the same step and read the same way in the brackets.

Extensions live in a folder inside the app data on this computer, and the Extensions screen opens it with one button.

Antivirus took the files

Security software that watches new folders can hold or quarantine one in the middle of a move. An extension archive is an ordinary archive and is sometimes treated as suspicious because of where it is being written.

The previous version is kept

A version already installed is set aside before the new one moves in, and it is put back when the move does not finish.

A failed install leaves the working copy alone

The old folder is moved aside rather than deleted, and it returns when the replacement cannot take its place. Profiles that were using it keep using it.

Collecting the evidence

Close every profile, press Install once more, and copy the whole line including the words in brackets: those words are the cause.

Write from the Support screen and name the extension. The report that travels with the message carries the version and the system, and no cookies or keys.

What this article does not cover

An archive that would not unpack. That is a different line and it happens one step earlier.
An old kind of extension. Only the third generation is accepted, and the refusal says so by name.
An extension that installs and then does nothing. On the built-in engine blocking rules are quiet and the card says so.

Where this is decided

Each claim above is one place in the code and one stand.

An archive is unpacked with a real archive and cannot write outside its own folder: apps/desktop/test/extension-install.js
A folder name from outside is never trusted as a path fragment: apps/desktop/test/extension-paths.js
An extension installed from the store keeps its store identifier: apps/desktop/test/ext-keeps-store-id.js
An enabled extension never promises more than the engine does: apps/desktop/test/extension-limits-honest.js

Questions

Does this mean the file was tampered with?: No. The signature and the identifier are checked before this step, and a mismatch carries its own line saying nothing was installed.
Where do extensions live on my computer?: In a folder inside the app data, one directory per extension. The Extensions screen opens that folder for you.
Can I put the files there by hand?: Yes. A folder named exactly as on the card with a manifest inside is loaded when the profile starts.

Next to this

Still stuck

Support reads the report that travels with your message and answers with the cause, not with a checklist.

Contact support Knowledge base