Go to SEC.gov and read the many litigation releases and the like. U.S. trading rules (But not laws) don't allow shorting certain stocks but I think Canadians and others can do it if shares can be borrowed.
Shorting any stock is risky; I've never shorted a stock. Shorting creates short term gains, not LT capital gains that are tax-favored. But if you're an insider with a garbage stock and control it, especially the dilution, you can short your own company with almost total confidence. From what you've posted, MMRF looks clean on that score right now.
The more you know about stocks, the more you stick with the highest quality stocks!