I've been a long time Firefox user (due to multi-row tab extension -- can't live without it). I can easily have 120 tabs open when doing research. Firefox has always been relatively performant even with that huge number of tabs visible and I almost never have to close it.
However, something recently has changed. Firefox will work fine and then something will cause it use a large amount of CPU that it doesn't let go of even after closing all the tabs. I have to close the whole browser and re-open it. This can happen a few times a day.
I'm hoping it's a regression that will be fixed soon.
Use one or more of these with the Session Manager [4] extension and life becomes a lot easier with several hundreds of tabs. I highly recommend looking at the configuration options provided by each of these extensions and adapting them to how you'd like them to behave. Some of these are also developed with compatibility with the other extensions in mind.
However, something recently has changed. Firefox will work fine and then something will cause it use a large amount of CPU that it doesn't let go of even after closing all the tabs. I have to close the whole browser and re-open it. This can happen a few times a day.
I'm hoping it's a regression that will be fixed soon.