The Share on Twitter bookmarklet from https://dev.twitter.com/web/bookmarklet often has a blank box. Nearly always blank when used to share Wikipedia. Blank used to share https://medium.com/@PresidentObama/my-plan-for-a-free-and-open-internet-c45e2f4ab1e4 . It’s failed in this way for years in numerous versions of Firefox. The share box exists, it’s just empty. It was empty for wordpress.com, unlogged in, but worked for http://afinedayforanepiphany.wordpress.com/2014/11/04/chiseling-down-the-wall-my-berlin-wall-memories/, also unlogged in to wordpress.
Just installed in Chrome, and and it failed with an empty box on Wikipedia.
Just installed it in Internet Explorer and it failed trying to share Wikipedia and http://peacekeeper.futuremark.com/results?key=9obx&resultId=5276552 but not with a blank box, in this case it shows “The webpage cannot be found HTTP 400”.
Third party share bookmarkets that work exist but one that only involves Twitter in sharing to Twitter is nicer.