最好确认下后面还有没有其他的报错信息,一种可能是系统是64位的,你下载的是32位的firefox,所以没法执行32位的命令
./firefox: cannot execute binary file. The info returned by file is as follows:
firefox: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV),
dynamically linked (uses shared libs), for GNU/Linux 2.6.9, stripped