I've written DropboxDiff, a Chrome extension which allows you to compare different versions of text files you have on Dropbox. It basically triggers a diff tool you have installed on your local machine already, which you must configure.
- On the Dropbox website, browse to the "Previous versions" page of any text file.
- A "Diff" column has been added where you can select which two versions to compare.
- Click the "Diff" button.
- If a diff tool is not yet configured, the options page opens where you can specify one. If you don't have one installed already, I recommend kdiff3. The setting is accessible from Tools > Extensions > DropboxDiff > Options.
- Otherwise, your diff tool should open.
This should run on Windows, Mac, and Linux. Please let me know if any issues come up.