Spontaneous window size changes

I am running osX10.7.5. on a mid-2009 MacBook Pro (with Firefox 34.0.5, but this is not a Firefox issue). Suddenly the window size of some windows change spontaneously to unchangeable small sizes that often cut off some of the content folders. The size cannot be corrected. The Toast Titanium burn window became too large to reach the lower size-change point. A restart has fixed this, but the problem persists now and then. Any ideas? Thanks!