1) Can I use ALE to toggle /CE since FRAM require max active /CE at 10000ns? ...2)
How to prevent accident write to FRAM during power loss if I don't have mechanism to detect power failure
1) No. Assuming the FRAM is your only data memory and you use extrenal code memory I would invert !PSEN to FRAM !CE - that does not make logic sense, but would work very well. On the other hand, if the above is not so come back, there are other ways.
2) When using non-volatile memories I like to use two supervisor chips. set your power supply a diode drop over Vcc feed the Uc through a diode and have a fat cap across the uC. One supervisor before the diode will interrupt the uC when power goes down, the other kicking in a bit later will reset the uC.

Erik