If you’re using 32-bit Firefox on 64-bit Windows, with 2 GB or more RAM installed, your Firefox will be automatically updated to 64-bit. Mozilla has specially released Firefox 56.0.1 for this purpose.

If you prefer to run 32-bit Firefox after 64-bit migration, you’ve to run Firefox 32-bit installer and Firefox will not try to migrate 32-bit users running Firefox 56.0.1 or later to 64-bit.

After automatically updating 32-bit Firefox to 64-bit, Firefox sets a key ’32to64DidMigrate’ in the registry and assigns its value as ‘1’.

So next time, if the Firefox update sees this key value as 1 (which conveys Firefox has migrated from 32-bit to 64-bit on this machine) Firefox then skips the migration process if you’re using 32-bit Firefox.

Firefox 51: About window tells your Firefox is 32-bit or 64-bit

To prevent or stop 32-bit Firefox from auto updating to 64-bit

1. Open registry editor

2. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Mozilla\Firefox

3. Create a new key named32to64DidMigrateand give DWORD 32-bit value name as ‘Never’ and Value data as ‘1’.

Go back to 32-bit Firefox from 64-bit after migration

  1.  Visit Firefox Platforms and languages download page
  2. Download 32-bit Firefox 56.0.1 Windows version and install it on your computer.

Note: Mozilla is currently planning to migrate eligible Firefox 56.0 win32 users to Firefox 56.0.2 win64.