If you are convicted for simple possession of marijuana or possession of a small amount of marijuana, those are both misdemeanors. If either of those offenses are the sole offense on your record, you will not lose your right to vote. 25 Pa.C.S. sec. 1301(a) states that only those potential voters who have been incarcerated for a felony within the last five years are ineligible to vote. In other words, if you’re locked up on a misdemeanor, you can still vote from jail in Pennsylvania.
As for firearm rights, you won’t lose those either. Under 18 Pa.C.S. sec. 6105(c)(2), you are unable to lawfully possess a firearm if you were convicted of an offense under the Controlled Substances Act that was punishable by two years of prison or more. Possession of a small amount of marijuana has a 30-day maximum. Simple possession of marijuana has a one-year maximum. So either way, you won’t lose your firearm rights under Pennsylvania law.