Fix popup showing when highlighting

[eranhirs]

Following issues #16, #28 and welpdx#3

[eranhirs]

Until something like this pull request is merged, if someone wants to use this you can clone my fork, change to the branch fix_popup, and run the bin/build.sh file. This will create an .xpi file that you can use.

[FrLars21]

@eranhirs I just refactored this plugin to work with Zotero 7, while also adding a lot of enhancements (better error messages, custom "citation count" column etc.). Since this repo seems unmaintained and because Zotero 7 bootstrapped plugins are fundamentally different, the code is hosted here. Would you care to submit a PR to that project with this bugfix, so that you can be properly credited?

[UrsaSense]

Please update to the latest xpi file, thank you very much

[eschnett]

@eranhirs I am not putting enough time into maintaining this repository. Are you interested in becoming a collaborator so that you can merge PRs yourself?