I was trying to play a MIDI track on Firefox, and this happened:
SUSE Paste
Which would translate:
“A program needs an additional add-on for this operation.
The following file is needed:
audio/midi decoder
Do you wish to search it now?”
I clicked “search” but it returned “couldn’t find the needed add-on”, or something like that.
Am I missing some other multimedia codecs/packages? I installed multimedia following mr Caf’s guide. Installed all packages from this guide.
Thanks beforehand.
I too get the same error i can give you a workaround. But you will not have any player control 
But you can play files
install timidity
http://paste.opensuse.org/images/31380058.png
This screenshot is from SeaMonkey but Firefox too has a similar setting.Search for midi and Choose “other”
http://paste.opensuse.org/images/48222732.png
Set Timidty as helper application
With Konqueror, I simply click on the midi file and Konqueror offers me the option to play it with timidity - no need for any plugins or addons.
A MIDI file isn’t an audio file as such and thus does not need any codecs to work; it only holds information such as key, amplitude, tempo etc. (possibly also instrument in the case of general MIDI) similar to a written score. You need a player with access to a sound bank which can transform that information to sound using whatever instrument from the sound bank you wish it to use, like timidity can.
Are there any other alternatives aside Timidity?
Vazhavandan’s suggestion looks good, but as he says, it’s more of a workaround rather than a solution.
Besides, I’ve installed Timidity before, back on openSUSE 12.2 in order to make music to work on Doomsday (playing Ultimate Doom, for example), but music tracks played with quite a different tone in comparison with Windows, as though they were a “remastered” or a different version, and it was not the same. I think it was probably because of Timidity…
No ,it is not due to timidity but as F_Sauce has pointed out
A MIDI file **isn’t an audio file **as such and thus does not need any codecs to work; it only holds information such as key, amplitude, tempo etc.
I’m not sure how to best play MIDI files from the browser, most likely you will end up with whatever MIDI file you play having whatever instrument the player, e.g. Timidty, you use are set to use; hence, it will be a possible strange listening experience and maybe a strange practise if one wish to enjoy the tunes. Fluidsynth is an alternative to Timidity, Audacious, and also XMMS2 I think, has a Fluidsynth plug-in which enables the player to play .mid files; but going about it this way (opening the file with Audacious from the browser) will be rather similar to using Timidity.
If you wish to have more control you could try downloading the MIDI files and use a MIDI sequencer along with Fluidsynth/QSynth (which in my opinion is easier than Timidity) and a GM sound-font to play them with; this makes it possible for you to assign the ‘correct’ instrument for the various channels on the different tracks, as you wish, selected from the GM bank; or selected from a different sound-font or synthesiser you wish to use. QSynth is a GUI for Fluidsynth and it is quite easy to set up.
Cheers and good luck.