Hello, at the moment, there are two known issues (one in Tab Stash and one in Firefox) that can lead to high CPU usage and which I'm looking into for the next Tab Stash release. Fortunately, there are workarounds for both.

First, if you upgraded to Tab Stash 2.10 from an earlier release and you notice high CPU usage after the upgrade, please try uninstalling/reinstalling Tab Stash (simply disabling it isn't sufficient). Pre-2.10 versions had a bug which left some stale deleted-items entries around, and when you first upgrade to 2.10, those entries will be cleared all at once, resulting in the high CPU. Uninstalling/reinstalling Tab Stash is another, faster way to clear out the old entries.

Second, there is a bug in Firefox's saved session handling which can cause Tab Stash to have high CPU usage. Tab Stash tries to work around this bug, but the workaround is what causes the high CPU. The bug seems to have gotten worse in recent Firefox releases and so I'm looking at ways to improve the workaround. In the meantime, however, clearing out any invalid saved-session data usually resolves the problem; you can find instructions here:

https://github.com/josh-berry/tab-stash/wiki/Restart-Firefox-Without-Saved-Session-Data

If neither of these things helps, please feel free to open an issue on GitHub and I'd be happy to troubleshoot further with you there.