For some time I had noticed that writing in Gmail had become slow and unresponsive, but even worse were the mouse operations of selecting text and opening contextual menus with the right click.
I thought it might be due to some add-on that performs on-the-fly operations like SimpleTranslate that offers translation popups on the selected text, but no… I have disabled it and nothing has changed.
So, I deactivated extension after extension without any improvement, until I deactivated UI.Vision (v6.2.6) and thus the problem disappeared in an eye-blink!
(issue found for sure on Firefox 105 and later, but may have been present from earlier versions)
I tested with Firefox V108 and Gmail and for me all works fine. => Did you try to reinstall UI.Vision? Does the issue then show again?
Yep… I have also started from scratch with a fresh new Firefox profile and this issue still remains.
You can also experience this slowdown simply by starting to write a new message in Gmail: paste any pre-existing text, perhaps long enough to do this test, try selecting a portion of this pasted text and then undo the selection by clicking somewhere outside it.
You will notice that both the selection by mouse seems unresponsive, and the cancellation of the text selection will occur with some delay.
Then repeat the same test with the UI.Vision extension disabled and you should notice an astonishing difference in responsiveness.