Not X10 switches. If I had to put a filter on them I don't know where it would. There certainly isn't room in the electrical box and the electronic switches are so big they almost didn't fit. The switches are also timers. Quite large.
The Leviton 6287 is pretty small: 1.6" x 1.9" x .8" thick. I had no trouble squeezing them in behind the Leviton X10 switches here (which also are pretty large). Unfortunately, many electrical contractors put in the smallest electrical box allowed under the code. If your switch box is too small, you might be able to fit the filter into the junction box for the first light in the string. It wires in series with the switched hot lead, with a connection also to neutral.
The switching circuitry in CFLs can vary with line voltage and temperature. A recent combination of those variables may have moved the frequency right on top of the X10 carrier frequency.
Jeff
