Where do these ideas come from.
If plugs then motor will not be running evenly, plugs on these show bad under load first meaning if you waited till it showed up at idle you are blind indeed. Fuel filter shows up under load first too........
Whynot (luv ya!) is speaking of test for a VISIBLY BROKEN mount, these cars can commonly vibrate when mount gets loose but not broken. Test is useful but does not necessarily mean everything. The pass side almost never broken externally but is in effect inside. It may look fine but be dead. DON'T buy anything other than Ford part, the aftermarket has shown repeatedly they cannot make quality long lasting mounts for these cars. Many will vibrate worse than your broken one right out of the box.
People seem to think for some arcane reason that if they can see the motor vibrate visibly that means something? Nope. If the damper method is working correctly there is no way you can correlate engine movement to actual vibration going into the chassis. ALL 4 cylinders vibrate unless they are equipped with balance shaft. A function of engine design.......
Too light a body? You gotta be kidding. More like they cheaped out and dropped the 4th engine mount that would have stopped all of this. All earlier Ford FWD compacts had 4 point mounts instead of the 3 on these and they don't shake badly even when one mount torn in half. The body itself has a pretty substantial subframe running all the way around the front. Ford yanks engine/trans by putting a hoist on top of the inner fenderline, which speaks scads of how stiff and stout the front box is.
To OP, if you think mounts do the passenger side one first, that one almost always gets the most result. The back of trans mount easy enough to diagnose, when driving if you feel a clunk when getting on or off power at times, well there it is. Never seen one bad on these that didn't show up there first. Pull airbox and look for rubber crumblies all around the trans top mount, you can often see the top cross bar has separated from the rest of the mount.