This just happened to me too - I think firefox automatically updated itself (I now have version 52.0.2). Unclear whether "tiddlyfox" also updated itself - it now seems to be called "tiddlywiki for firefox". As Zyb says, the download dialogue was triggered but the wiki appeared to otherwise save as normal.
The blue/green ball has motovun jack stood on it and looks like this <https://lh3.googleusercontent.com/-4H1LKi-3JY8/WO7Lzy9J3GI/AAAAAAAABsQ/-wurXfK41hcB3vE-ez2RaP_fBB9OZ_vIgCLcB/s1600/Screen%2BShot%2B2017-04-13%2Bat%2B10.48.23%2Bam.png> Regards, Richard -- You received this message because you are subscribed to the Google Groups "TiddlyWiki" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/tiddlywiki. To view this discussion on the web visit https://groups.google.com/d/msgid/tiddlywiki/3026987f-d15d-4637-b9b9-4c8560dfdfe3%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.

