What part of Mozilla? Our websites? Mozilla.org uses 128-bit encryption with TLS 1.2

The OP likely meant Mozilla Firefox or Firefox as it has supported 256-bit for a long time. The Firefox useragent used to have the U in useragent (before Firefox 4.0 ?) as it was the obsolete way of telling sites it supported 128-bit at minimum.

On a tablet so finding and posting relevant links is a chore.

edit: All Firefox versions have been supporting AES 256 bit ever since it was Firebird 0.6, May 2003

NHsky01 said

Hello, Does Mozilla use 128 bit encryption? I'm unable to find out what level it uses. Thanks, Ruth

The browser portion. I'm clearly not a tech so appreciate your help. I'm looking to file employer paperwork re quarterly taxes for a small business. To do this, apparently I need 128 bit encryption to be used by the browser I use. I prefer Moxilla for everything. Thanks, Ruth

NHsky01 said

The browser portion. I'm clearly not a tech so appreciate your help. I'm looking to file employer paperwork re quarterly taxes for a small business. To do this, apparently I need 128 bit encryption to be used by the browser I use. I prefer Moxilla for everything. Thanks, Ruth

As I said Firefox supports 256-bit encryption even for almost twelve years now.

If the website you are using claims Firefox does not support even 128-bit then it may be incorrectly looking for the obsolete U that was in Firefox useragents in past to show sites it supported 128-bit at minimum. It should not need to since 2002 even.