Fix firefox ability to load file, add firefox tests back (#1380)

## Launch Checklist

This PR fixes the problem with firefox not able to load a file when
clicking the open file button.
It does so by removing a very old dependency: `react-file-reader-input`
It uses the "regular" `<label><a/><input type="file" /><label>`
approach.
It adds tests for both firefox and chrome although I'm not sure the
firefox tests will stay...

 - [x] Briefly describe the changes in this PR.
 - [x] Write tests for all new functionality.
 - [x] Add an entry to `CHANGELOG.md` under the `## main` section.

package.json

@@ -66,7 +66,6 @@
     "react-collapse": "^5.1.1",
     "react-color": "^2.19.3",
     "react-dom": "^19.1.1",
-    "react-file-reader-input": "^2.0.0",
     "react-i18next": "^15.7.3",
     "react-icons": "^5.5.0",
     "react-markdown": "^10.1.0",
@@ -118,7 +117,6 @@
     "@types/react-collapse": "^5.0.4",
     "@types/react-color": "^3.0.13",
     "@types/react-dom": "^19.1.9",
-    "@types/react-file-reader-input": "^2.0.4",
     "@types/string-hash": "^1.1.3",
     "@types/uuid": "^10.0.0",
     "@types/wicg-file-system-access": "^2023.10.6",