Multiple actions on a page browser support issue

Reproduction

Here is my reproduction repository: GitHub, based on Remix's Multiple Forms example. My repo uses the latest version of Remix, and I was able to reproduce the issue in both Remix v1 and v2. The issue seems to occur with browsers that do not support the SubmitEvent: submitter property. I reproduced it with Firefox 74 since I can't install Safari on Windows.

We are aware that these are older browsers, but our application must support them to serve Canadian citizens, and it is challenging to force users to update their browsers. Safari 15.4 was released on March 14, 2022, and we believe supporting at least Safari 15 is necessary. User metrics indicate this issue also occurs with other browsers that lack submitter support, including:

Safari 14 with over 50% of the errors collected
Safari 15 (version 15.4 has full support for the submitter property)
Safari mobile 14
Safari mobile 15
Chrome Mobile 125

System Info

System:
    OS: Windows 11 10.0.22631
    CPU: (8) x64 11th Gen Intel(R) Core(TM) i5-1145G7 @ 2.60GHz
    Memory: 5.21 GB / 15.69 GB
  Binaries:
    Node: 20.15.0 - C:\Program Files\nodejs\node.EXE
    npm: 10.2.5 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Chromium (126.0.2592.81)
    Internet Explorer: 11.0.22621.3527
  npmPackages:
    @remix-run/dev: ^2.10.0 => 2.10.0
    @remix-run/node: ^2.10.0 => 2.10.0
    @remix-run/react: ^2.10.0 => 2.10.0
    @remix-run/serve: ^2.10.0 => 2.10.0
    vite: ^5.1.0 => 5.3.3

Used Package Manager

npm

Expected Behavior

When a page in Remix contains multiple actions and a user submits a form, the form data should include the intent key, with the value corresponding to the intent value of the action submitter.

Actual Behavior

The actual behavior is that the intent key is not present in the form data.

remix-run / remix