From LightWiki

The FX Browser is another way of interacting with dynamics in LW. When you have it open it has some advantages over going through the Object Properties Panel dynamics tab:

• When you select a dynamics object, it automatically opens a window for the settings for that object. Also, if you have a tab selected for one item, and select another item of the same dynamics type, that tab is kept selected. In the OPP, if you select a new dynamics item, you have to select the tab again. This is handy if you're adjusting a lot of items using just one tab.
• The Calculate function is more robust in the FX browser than just using the OPP Calculate button. If you switch to another application while the calculation is in progress, then switch back, the FX Browser will refresh the view, so you can see what stage the calculation is up to. The standard Calculate will only refresh Layout once the calculation is over, which can look like Layout has crashed, especially if the calculation is taking a long time. Also, the Abort button tends to be more robust, with less likelyhood of LightWave crashing.