For your telescope I'm reading different statistics on Celestron's website than the ones you posted in your question:
Highest Useful Magnification 180x
Lowest Useful Magnification 11x
I'm new to this. Could someone tell me if I'd be able to see planets
with the Celestron Cometron FirstScope?
You can see the planets with your eyes in a clear sky (even with some light pollution). They look like colorful stars that don't twinkle. In a telescope of low magnification and poor build quality you can also see the planets: they just look like bigger disks of light without recognizable details. The question you're not asking is "What do I need in order to see the details of the planets?" or "What do I need in order to get spectacular views of the planets?". I'm including an excellent answer to this follow-up question from a separate post to this site:
As a general rule, there isn't much point in pushing the magnification
above 2x the diameter of the instrument, measured in mm. 3 inch,
that's 75mm, that's 150x max. Beyond that limit, even under ideal
skies the image is large but blurry.
After that, seeing (or air turbulence) pushes that limit further down.
Your aperture is small enough that it almost never suffers from
seeing, but larger instruments are often affected. It varies greatly
with time, place and season. There are times when a 12" dobsonian,
that in theory could do 600x, is clamped down by seeing to 150 ...
180x. There are times when you could take a 20" dobsonian all the way
up to 1000x - but that's very, VERY rare, it's the stuff of legends.
Assuming average seeing conditions and instruments of usual size
(refractors of 3...4" aperture, reflectors 6" or larger), here are
some rules of thumb:
Jupiter is seen best under mid-high magnification. It's rare that more
than 200x is beneficial. This is because it's a very low contrast
object, and additional magnification comes at the cost of less
contrast, which makes things worse.
Saturn works best at high-ish magnification, bit more than Jupiter but
maybe not much more. Around 200 ... 250x usually works. It depends on
what you do - if you're trying to see the ring divisions, push it a
bit higher.
Mars can use the highest magnification that you could generate, given
the instrument and the conditions. It's a very small object, contrast
is not bad, so crank it all the way up. Most instruments are limited
by seeing when observing Mars.
Moon is the same as Mars.
As you can see, magnification is never an issue for you. More
magnification will not make it better. In fact, more magnification
always means the image is more blurry, not more crisp - it's always a
compromise between size and blurriness that decides the optimal
magnification.
Assuming this reasoning is correct in your case, it looks like you'd be able to see Jupiter with this telescope in some detail, but perhaps not the other planets with any helpful level of detail.
As a side note, I'd strongly recommend replacing those Kellner eyepieces with something better (Plossls or better). And quite frankly, if planetary viewing is your passion, I'd look into saving for a refracting telescope and eyepieces of high quality rather than a budget starter kit.
