Update User-Agent strings for Firefox/Opera/Chrome/Edge - #793

I checked the current head 25dfb510 against current master.

Local checks:

go test ./extensions -count=1
go test ./... -count=1
git diff --check origin/master...HEAD

Those pass. gofmt -l extensions/random_user_agent.go still reports extensions/random_user_agent.go.

I think the update still needs another pass before it matches the maintainer request to use latest supported version strings:

• The added lists stop at Firefox/Chrome 119. Current official feeds I checked report Firefox 151.0.3 / DevEdition 152.0b6 from https://product-details.mozilla.org/1.0/firefox_versions.json, and Chrome stable Windows 149.0.7827.54 from ChromiumDash.
• One added Chrome entry is release-note shorthand rather than a UA-safe version: 114.0.5735.90/91. Since genChromeUA emits it as Chrome/%s, that can produce Chrome/114.0.5735.90/91 Safari/.... A local-only guard test over chromeVersions failed on that exact value.

So I would refresh the data against current supported versions, split/remove shorthand entries, and add a small guard test for UA-safe Chrome version strings.