Sends beacon request in beforeunload event in Firefox

[mstahv]

Firefox has a bug/feature that it don't send the beacon in pagehide event.

Fixes #19305

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.

Additional for Feature type of change

• Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[github-actions]

Test Results

1 141 files  ± 0  1 141 suites  ±0   1h 23m 29s ⏱️ - 4m 36s
7 447 tests ± 0  7 397 ✅ +22  50 💤 ±0  0 ❌  - 10 
7 819 runs  +15  7 759 ✅ +37  60 💤 ±0  0 ❌  - 10 

Results for commit e4af719. ± Comparison against base commit 1fbf412.

♻️ This comment has been updated with latest results.