Since Atlassian seems incapable of fixing the most basic CSS errors, for anyone looking for a workaround, you can setup a userContent.css in your Firefox profile with the following, this overrides bitbucket.org paragraph styling to always use 0 letter-spacing, which should be fine since Atlassian don't seem to know how to use it appropriately anyway:

@-moz-document domain(bitbucket.org) {
    p {letter-spacing: 0.0em !important;}
} 

Reference: https://superuser.com/a/319322

Come on Jira team, just get rid of that letter-spacing and commit it.

I have run across this multiple times over the past 3 weeks after switching to using Firefox.

I am just here to bump this as another person to notice the issue.

The font is difficult to read in Firefox and is having an impact on our users with accessibility issues. 

As an example I've created a ticket with lorem pisum placeholder text in it, and the difference between Chrome and Firefox makes it quite obvious where the testing is and isn't happening. 

Chrome:

Firefox:

We've come across a number of tickets that use the work "click" and it does lead to some confusion when reading the tickets for the first time...

This seems to be caused by a bit of CSS applied to `p` tags:

letter-spacing: -0.005em;

Obviously not critical, but it is strange. Write "clunky" and it appears as "dunky"...