Acid Injector converts MIDI clips generated by STING by IFTAH (free Max For Live device) into .seq pattern dump files so you can use Behringer's Synthtribe software to send them to your TD-3 (Roland TB-303 clone). It also generates .syx (sysex) files so you can send a pattern to the TD-3 using any sysex librarian software or sysex-friendly DAW such as Reaper.
It's browser-based, but pure Javascript and no WebMIDI or server communication is involved - it just reads and writes bytes, turning MIDI files into .seq/.syx files on the fly.
If you want a more feature-rich and aesthetically TD-3 manager, check out the awesome 303patterns.com by AudioPump. I found it to be a bit fussy about my admittedly complex and bewildering MIDI driver(s) situation, plus I made Acid Injector before I knew about it, but you might find it suits you better!