Browser spelling checkers
Internet Explorer / Edge
Sorry, no support - YET. It requires an OS-wide speller, which should in principle be possible since Windows 8. We are working on it, but it has turned out to be harder than anticipated. We'll update the page as soon as we have news.
Firefox
Firefox needs its own proofing tools, which are installed as extensions in Firefox. There are actually two sets of Firefox spelling plugins, one made by Tino Didriksen, and another built using Mozvoikko. The Didriksen spellers only work on Windows (for now), whereas the MozVoikko spellers work on both Windows and OSX. Using MozVoikko, one can install multiple languages.
Firefox on Linux
The MozVoikko speller is available on Linux, but you have to build it yourself. Further instructions can be found on the page for installing spellers OS wide.
Chrome
Sorry - no support. Chrome uses Google's own spelling checker, which we don't have access to. And Google does not support the languages we are working on (please prove us wrong, Google!).
Safari
Safari uses the OS-wide spelling service in OSX. See the download options on the page for OS-wide spelling checkers.