Summary

Adds the same startup retry logic that Chrome/Edge already have to the Firefox (geckodriver) path.

Problem

GetFirefoxDriver uses CreateWebDriver which tries once and throws on failure. GetChromiumDriver has a 3-attempt retry loop. When geckodriver takes time to bind to its port, xharness gets repeated Connection refused errors followed by WebDriverException: Cannot start the driver service and exits with code 71 (GENERAL_FAILURE).

This is a known CI flake pattern — dotnet/runtime#104349 tracked the same Connection refused issue and had BuildRetry: true as a workaround.

Example from dotnet/runtime build 1365445:

Connection refused [::ffff:127.0.0.1]:42115 (localhost:42115)
... (repeated ~45 times)
geckodriver INFO Listening on 127.0.0.1:42115
OpenQA.Selenium.WebDriverException: Cannot start the driver service on http://localhost:42115/

Fix

• Add retry loop (3 attempts) to GetFirefoxDriver matching the Chromium pattern
• Catch WebDriverException with known retryable error snippets: Cannot start the driver service, Connection refused, exited abnormally, failed to start
• Enable verbose geckodriver logging per attempt for diagnosis
• Properly dispose driver service on failure before retry

Prior art

• e439337 — Chrome DevToolsActivePort retry fix (same repo)
• [browser] Connection refused in 127.0.0.1 runtime#104349 — [browser] Connection refused KBE
• Known Build Error: Blazor SimpleRunTests/BlazorBuildRunTest Playwright timeout on Counter click runtime#126489 — Playwright timeout KBE