I've developed a LanguageTool extension for Chrome. It lets you check texts in Chrome from either input fields or selected text. Please give it a try and post your experience here in the forum:
It's still an early release, so you should expect that it's not totally free of bugs yet.
For those not using Chrome at all: our Firefox add-on can be found at https://addons.mozilla.org/en-US/firefox/addon/languagetoolfx/