While manually testing the patch in bug 675539 I hit a race by unloading multiple tabs in a short amount of time while switching between them (note: the machine was under heavy load hence the UI was quite slow to respond).

Since I was quickly cycling through tabs I might have switched to a tab that was about to be unloaded, or maybe I just switched to a tab that had just been unloaded, I cannot be sure which. However I got an exception from AsyncTabSwitcher.jsm where the tab's frameLoader field was null. Unfortunately I haven't saved the log; I'll try to reproduce the problem and attach it here.

From an end user perspective (without looking at exceptions), what might be a symptom of this bug?

The tab remains empty even though it should either contain a page or reload one that was just unloaded.

The severity field for this bug is relatively low, S3. However, the bug has 43 votes.
:dao, could you consider increasing the bug severity?

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