I'm pretty sure that merely tab-switching hasn't fixed it for me. I've done both mouse and alt-tab, i've ctrl-w'd the tab and ctrl-shift-T'd it. I've opened the same site in a new tab and it still wouldn't work. I've had to completely shut the browser down. Maybe it's different between Windows and Linux, perhaps (I'm using Windows for this).

Maybe there's more than one cause, but the reason I hate this bug so much is because simple fixes like just alt-tabbing or even closing and re-opening or full-reload doesn't work. I'm like 99% certain that's the case. I'll have to verify next time this happens. It seems to happen at least a couple times a month.

Or just hold down shift, at least in Firefox. This avoids sending the events to the javascript on the page so that the user can act on the page without being blocked, while still using a page’s own context menu if it really does provide a useful one (Google Docs, for example, has one with actual editing actions in it).

Firefox does it best here, because you can hold shift to get the original context menu back when the page blocks it or provides their own.