using 3/20 build of netscape 1) launch netscape 2) launch composer 3) insert text 4) highlight text 5) increase font size 6) descrease font size 7) hit bold button notice your selection is gone....I showed this behavior to Joe in my office. all platforms.
This sounds a lot like #29533; although the test cases are slightly different I am betting it's the same bug. Setting to M15 since I'm guessing/hoping Joe has fixes in his tree.
verified in 3/28 build.