What is the PCV file format?
.pcv is a backup copy file associated with the user profile format used by various Mozilla products. .pcv files are generated by the MozBackup tool and can store user profile data for applications such as:
- Mozilla Firefox
- Mozilla Thunderbird
- Mozilla Suite
- Netscape
MozBackup was a useful tool for transferring user settings across applications and computers, though it is no longer actively maintained and does not support modern Firefox or Thunderbird profile structures.
A .pcv file is a standard ZIP archive with a renamed extension - it can be unpacked with any archiving software that supports ZIP compression, including 7-Zip, simply by renaming the file to .zip. MozBackup copies all relevant profile data (bookmarks, preferences, mail, cookies, stored passwords) into the archive. Using MozBackup itself remains the most reliable method for restoring a .pcv backup to ensure profile data is applied correctly between applications. Note that MozBackup 1.5.1 - the last stable release - is incompatible with modern Firefox and Thunderbird.
Security & safety
RISK: LOWA .pcv file contains your Mozilla profile data, which may include saved passwords (encrypted by Firefox/Thunderbird's own NSS encryption), cookies, and browsing history. The archive itself is not dangerous, but treat it like a sensitive backup: keep it private, as its contents include personal data. The saved passwords inside are encrypted and not trivially readable without the master password, but the encryption strength depends on your Firefox settings.
Format details
in a nutshellPrograms that open PCV files
Windows4 apps
MozBackup
Free Install MozBackup and use its Restore function to restore to a compatible Mozilla application profile. Caveat: abandoned and incompatible with modern Firefox/Thunderbird. 
7-Zip
Open-source Right-click the .pcv > 7-Zip > Open archive. It is a ZIP - browse and extract any files inside. No rename needed. 
Windows Explorer (rename trick)
Built-in Rename .pcv to .zip, then double-click in Windows Explorer to open the archive and extract files. Technical details
deep spec| Container format | Standard ZIP archive (PKZIP format) with `.pcv` extension |
| Magic bytes | `50 4B 03 04` ("PK") at offset 0 - standard ZIP local file header |
| Compression | DEFLATE per-entry ZIP compression |
| Byte order | Little-endian (ZIP format) |
| Integrity check | CRC-32 per ZIP entry (standard ZIP integrity) |
| Typical file size | 1 MB - 500 MB depending on profile size (mail, bookmarks, extensions, cache) |
| Profile data stored | Bookmarks (`places.sqlite`), preferences, cookies, stored passwords, extensions, and Thunderbird mail folders |
| Extraction method | Rename to `.zip` and extract with any ZIP tool (7-Zip, WinZip, Windows Explorer) |
| Supported applications | Firefox, Thunderbird, Mozilla Suite, Netscape, and Spicebird profile backups |
| MozBackup compatibility | MozBackup 1.5.1 (last release, ~2012) is incompatible with modern Firefox/Thunderbird profile structures |
| Operating system | Windows only (MozBackup was a Windows application) |
| ZIP entry limit | Up to 65,535 entries per archive (ZIP64 extension lifts this limit) |
| Released | Early 2000s (MozBackup tool for Firefox/Thunderbird) |
| Latest version | MozBackup 1.5.1 (last released; tool largely abandoned, incompatible with modern Firefox/Thunderbird) |
Community Q&A
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