I have been using Sun’s old Java 1.5.0_06 runtime for quite a while, there simply wasn’t a good reason to waste time updating it. When investigating a Java-related crash I decided to check whether it will happen with a newer runtime (1.6.0-b105 was current at that time). Surprisingly, the crash disappeared even though this crash happened in Gecko code and not in the Java plugin.
But what I find more interesting is the change in Firefox’ memory usage I observe since that update. Previously Firefox would use 250 MB of memory after a few hours. It wouldn’t change much after that, only after a week or two the memory usage would climb to 350 MB. Now with a current Java version the usual numbers for Firefox are 150 MB reserved memory and below. After using it for over a week without restarting I still saw only 190 MB.
This is another indication that plugins have a huge impact on browser’s stability and memory use. So far extensions have received most of the blame, but usually they only cause crashes if they trigger bugs in Gecko or plugins. And thanks to dbaron’s Leak Monitor extension memory leaks in extensions have become rare.