How to tell if need more ram?

1.5GB is plenty of RAN for web browsing with Linux. I'd look elsewhere for the problem. Have you checked the system logs, and any .core files?

You can watch memory usage of the system as a whole and individual processes with the "top" utility

There are multiple commands that will tell you memory usage. As a basic overview, I use `free -m`. If you are using a lot of swap space all the time, it's probably time to add more memory.

Maybe the RAM sticks are old in which case they might be giving problems. Even 512MB is enough RAM to run light tasks like word processing and simple web browsing. Less RAM would not be the cause of the issue.

Memtest time?

As said before, if you are using excessive swap space then it should be time to think about getting more RAM. Since writing to a disk is much slower then writing to memory.

Though if just those two applications are crashing, run them from the terminal and output the error and see what is going on.

Also, I prefer HTOP, it does the same thing as the top command, it just looks prettier :P