I’m using Firefox, I have only the g-mail open, and at times, things sort of lock up and the little CPU monitor runs up to 30%-50%. Usually, when things are moving smoothly, it’s down around the 1%-5% range. I know that programs run in the background. How do I determine which ones are slowing this all down and if I can afford to close them?
I’ve no expertise but will comment anyway. 
On my Windows 7 laptop I had similar problems. Task Manager, sorting by CPU% showed YCMMirage (or such name) and ONENOTE to be culprits — no idea if they were Trojans from a bad click, or just earnest programs behaving like malware, but I didn’t need or want either. Rather than disabling them during boot, it seemed as simple to End them whenever convenient.
That laptop broke and I’m running Windows 10 on a new machine. :eek: with no obvious similar problems … yet.
( 
if any Cygwin experts volunteer to help, I’d like to start a GQ thread How do I recover from a botched cygwin permission transition? )
Task Manager, look at the Processes tab. You may have to turn on the “show processes from all users” function. You can sort by CPU.
Personally I prefer Process Explorer to get more detail. It’s a free utility from Microsoft and what’s really cool is that it’s a self-contained executable which means you don’t have to install it, it just runs from a single file.
Either will show you the process(es) hogging your CPU resources. The real trick is interpreting them. That’s tricky and comes with experience. Google can be your friend. It really helps if you keep track of what you’ve installed on your computer, both programs and system features.
Identifying the problem is only half of the trick though. The other half is fixing it. That usually means uninstalling a program or feature (or plugin for Firefox?) or changing a setting in your operating system or a program. Again Google is a good start.
If you mean that it spikes temporarily and then reduces again, probably you’re seeing the garbage collector being run. It could be the javascript engine in Chrome doing it, since gmail will constantly be running some tasks to check in with the server. Eventually, it will detect that it’s got a bunch of trash lying around in memory and need to go through and clean up.
If you can’t find any other applications causing the spike (using the methods that others have commented on), I’d probably suggest switching to Chrome. They have better parallelization and garbage handling.